Are you tired of the constant buzzing and humming of noise in your surroundings? Well, you’re not alone. Noise pollution has become a major concern in today’s world, and it’s important to measure the noise levels to take necessary actions. But how is noise level measured? In this comprehensive guide, we will delve into the different methods and techniques used to measure noise levels, including sound meters, decibel meters, and more. We will also explore the importance of measuring noise levels and how it can help in reducing noise pollution. So, let’s get started and learn how to measure the noise levels around us.
Understanding Noise and Its Effects
What is noise?
Noise is an unwanted sound or a disturbance that can interfere with communication, hearing, or other activities. It can be defined as any sound or signal that is not intended or desired, and can be caused by a variety of sources.
Definitions and types of noise
There are different definitions and types of noise, depending on the context in which it is used. In acoustics, noise is defined as any sound that is unwanted or interferes with the intended sound. In electronics, noise is defined as any unwanted signal or interference that can affect the performance of a system.
Sources of noise
There are many sources of noise, including:
- Mechanical noise: caused by vibrations or movements of machinery or equipment
- Electrical noise: caused by electrical devices or systems
- Thermal noise: caused by temperature fluctuations or changes
- Background noise: caused by environmental factors such as wind, traffic, or nearby construction
- Human-generated noise: caused by human activities such as talking, laughing, or walking
It is important to understand the different types and sources of noise in order to effectively measure and control noise levels.
The impact of noise on health and well-being
Noise can have a significant impact on one’s health and well-being. Exposure to excessive noise levels can lead to various physiological effects, including hearing loss, high blood pressure, and stress-related illnesses. Noise-induced hearing loss is one of the most common effects of excessive noise exposure. Prolonged exposure to loud noise can cause damage to the hair cells in the inner ear, leading to hearing loss. This can be temporary or permanent, depending on the level and duration of exposure. Additionally, noise can also increase blood pressure, leading to hypertension, a condition that can have serious health consequences. Finally, noise can also contribute to stress-related illnesses, such as anxiety and depression, by disrupting sleep patterns and increasing levels of the stress hormone cortisol.
In addition to the physiological effects of noise, it can also have a significant impact on one’s psychological well-being. Noise can cause sleep disturbances, leading to fatigue and irritability. It can also cause increased levels of stress and anxiety, leading to decreased productivity and overall quality of life. In some cases, excessive noise exposure can even lead to post-traumatic stress disorder (PTSD) in individuals who have experienced traumatic events associated with loud noise, such as explosions or gunshots. Furthermore, noise can also have an impact on cognitive function, leading to decreased attention and memory. Children who are exposed to excessive noise levels may also experience developmental delays and behavioral problems.
Measuring Noise Levels: Basic Concepts
Decibel scale and noise measurement units
The decibel scale
The decibel (dB) scale is a logarithmic scale used to measure the relative intensity of sound or other physical quantities. It is based on the human auditory system’s perception of sound pressure levels (SPL). The scale is designed so that a 10 dB increase represents a tenfold increase in the physical quantity being measured, while a 20 dB increase represents a hundredfold increase.
Sound pressure level (SPL) and A-weighted decibels (dBA)
Sound pressure level (SPL) is the amount of sound energy that is perceived by the human ear, taking into account the frequency and intensity of the sound. It is typically measured in decibels (dB), with higher dB values indicating louder sounds.
A-weighted decibels (dBA) is a unit of measurement used to express sound pressure levels that is adjusted to approximate the human ear’s response to different frequencies of sound. This means that low-frequency sounds, which are perceived as less loud by the human ear, are weighted more heavily in the dBA scale, resulting in lower measurements for these sounds compared to the actual sound pressure levels. This is why dBA measurements may not always accurately reflect the actual perceived loudness of a sound.
Sound level meters and their uses
Sound level meters are devices used to measure the intensity of sound in decibels (dB). They are widely used in various industries, including construction, transportation, and environmental monitoring, to ensure compliance with noise regulations and to assess the impact of noise on human health and the environment.
Types of sound level meters
There are two main types of sound level meters:
- Type 1: These are also known as precision sound level meters and are used for accurate measurements in professional and industrial applications. They have a frequency range of 20 Hz to 20 kHz and meet international standards such as IEC 61672 and ANSI S1.4.
- Type 2: These are also known as general-purpose sound level meters and are used for general noise measurement applications. They have a frequency range of 100 Hz to 10 kHz and meet international standards such as IEC 61672 and ANSI S1.4.
Calibration and accuracy
It is important to calibrate sound level meters regularly to ensure accurate measurements. Calibration should be done using a known reference sound source, such as a calibrated sound calibrator. Calibration records should be kept to document the calibration dates, results, and any corrective actions taken. Accuracy of sound level meters can be affected by environmental factors such as temperature, humidity, and vibration, so it is important to take these factors into consideration when measuring noise levels.
Noise exposure limits and regulations
Noise exposure limits and regulations are put in place to protect workers and the general public from the adverse effects of noise pollution. These limits are established by governments and regulatory bodies to ensure that noise levels in the workplace and in public spaces do not exceed safe levels.
Occupational noise exposure limits
Occupational noise exposure limits are established to protect workers from the harmful effects of noise in the workplace. These limits are set by regulatory bodies such as the Occupational Safety and Health Administration (OSHA) in the United States and the Health and Safety Executive (HSE) in the United Kingdom. The limits are based on the maximum allowable noise exposure for workers over a specified period of time, typically 8 hours.
Exceeding these limits can result in hearing loss, tinnitus, and other hearing-related problems. To ensure compliance with occupational noise exposure limits, employers are required to conduct noise assessments and implement noise control measures where necessary.
Environmental noise exposure limits
Environmental noise exposure limits are established to protect the general public from excessive noise levels in public spaces. These limits are set by regulatory bodies such as the Environmental Protection Agency (EPA) in the United States and the World Health Organization (WHO) internationally. The limits are based on the maximum allowable noise exposure for the general public over a specified period of time, typically 24 hours.
Exceeding these limits can result in sleep disturbances, hearing loss, and other health problems. To ensure compliance with environmental noise exposure limits, governments conduct noise monitoring and enforce noise control measures in public spaces.
In summary, noise exposure limits and regulations are put in place to protect workers and the general public from the harmful effects of noise pollution. These limits are established by governments and regulatory bodies and are based on the maximum allowable noise exposure over a specified period of time. Exceeding these limits can result in serious health problems and is therefore strictly enforced.
Methods of Noise Measurement
Type A and Type B sound level meters
Type A sound level meters
Type A sound level meters are designed to measure sound levels in a wide range of applications, from industrial settings to environmental noise monitoring. These meters are often used by professionals such as acoustic consultants, environmental scientists, and engineers.
Type A sound level meters are characterized by their high accuracy and precision, and they are capable of measuring sound levels in decibels (dB) over a range of frequencies. They typically have a frequency weighting scale that allows for accurate measurements of sound levels across different frequency ranges.
One of the key features of Type A sound level meters is their ability to measure sound levels with high temporal resolution, which means they can capture very short-term sound level changes with high accuracy. This makes them ideal for measuring transient sounds, such as those produced by machinery or explosions.
Type B sound level meters
Type B sound level meters are designed for measuring sound levels in situations where the sound source is unknown or variable, such as in occupational noise exposure assessments. They are typically used by professionals such as safety officers, health and safety managers, and industrial hygienists.
Type B sound level meters are characterized by their ability to measure sound levels in real-time, with high accuracy and precision. They are also capable of measuring sound levels over a wide range of frequencies, and they typically have a frequency weighting scale that allows for accurate measurements across different frequency ranges.
One of the key features of Type B sound level meters is their ability to measure sound levels with high temporal resolution, which means they can capture very short-term sound level changes with high accuracy. This makes them ideal for measuring transient sounds, such as those produced by machinery or explosions.
Overall, Type A and Type B sound level meters are essential tools for measuring sound levels in a wide range of applications, from industrial settings to environmental noise monitoring. They are highly accurate and precise, and they offer a range of features that make them ideal for measuring sound levels in different situations.
Handheld versus in-situ sound level meters
Advantages and disadvantages of handheld sound level meters
Handheld sound level meters are portable devices that are designed to measure the sound level of a particular area. These devices are typically small and lightweight, making them easy to carry around and use in a variety of settings. Some of the advantages of using a handheld sound level meter include:
- Portability: Handheld sound level meters are small and lightweight, making them easy to carry around and use in a variety of settings.
- Cost-effectiveness: Handheld sound level meters are often less expensive than in-situ sound level meters, making them a good option for those on a budget.
- Quick and easy to use: Handheld sound level meters are designed to be user-friendly, with clear instructions and simple controls.
However, there are also some disadvantages to using a handheld sound level meter. For example:
- Limited accuracy: Handheld sound level meters may not be as accurate as in-situ sound level meters, particularly when measuring sound levels at low frequencies.
- Limited range: Handheld sound level meters may not be able to measure sound levels at very high or very low frequencies.
- Requires human intervention: Handheld sound level meters require someone to physically hold the device and point it towards the sound source, which can be time-consuming and labor-intensive.
Advantages and disadvantages of in-situ sound level meters
In-situ sound level meters are permanently installed in a particular location and are designed to measure the sound level of that location over time. These devices are typically more accurate than handheld sound level meters and can provide more detailed information about sound levels over time. Some of the advantages of using an in-situ sound level meter include:
- High accuracy: In-situ sound level meters are often more accurate than handheld sound level meters, particularly when measuring sound levels at low frequencies.
- Long-term monitoring: In-situ sound level meters can be left in place for long periods of time, allowing for continuous monitoring of sound levels.
- Automated data collection: In-situ sound level meters can be programmed to collect data automatically, reducing the need for human intervention.
However, there are also some disadvantages to using an in-situ sound level meter. For example:
- Cost: In-situ sound level meters can be more expensive than handheld sound level meters, particularly when considering the cost of installation and maintenance.
- Limited mobility: In-situ sound level meters are permanently installed in a particular location, which can limit their mobility and flexibility.
- Maintenance requirements: In-situ sound level meters require regular maintenance to ensure accurate measurements, which can be time-consuming and costly.
Frequency weighting and A-weighting
What is frequency weighting?
Frequency weighting is a method used to determine the noise level in a given environment by analyzing the distribution of sound frequencies present in the noise. This method takes into account the fact that the human ear is more sensitive to certain frequencies than others, and weights the frequencies accordingly.
How is A-weighting used in noise measurement?
A-weighting is a specific type of frequency weighting that is commonly used in noise measurement. It is used to correct for the human ear’s natural frequency response, which is more sensitive to certain frequencies than others. A-weighting assigns more weight to the frequencies that the human ear is most sensitive to, and less weight to the frequencies that the ear is less sensitive to. This results in a more accurate representation of the noise level as it is perceived by the human ear.
Measuring noise in different environments
Measuring noise in industrial settings
In industrial settings, noise is measured using sound level meters that are calibrated to measure the sound pressure level (SPL) in decibels (dB). The SPL is measured at different frequencies using a type-1 or type-2 sound level meter, which meets the requirements of the International Organization for Standardization (ISO) standards. The measurement is typically taken at the ear level of the worker, and the results are recorded in dB(A), which is the A-weighted decibel scale that takes into account the human hearing sensitivity.
Measuring noise in residential areas
In residential areas, noise measurements are taken to assess the impact of noise on the quality of life of the residents. The measurement is typically taken at the most affected room in the house, such as the bedroom or living room. The measurement is taken using a sound level meter that is calibrated to measure the SPL in dB. The measurement is taken at different frequencies using a type-1 or type-2 sound level meter, which meets the requirements of the ISO standards. The results are recorded in dB(A) and compared to the recommended noise exposure limits set by the World Health Organization (WHO) and the International Council for the Advancement of Sound (ICAA).
Measuring noise in transportation settings
In transportation settings, noise measurements are taken to assess the impact of noise on the environment and the health of the people. The measurement is typically taken at the most affected location, such as near a highway or an airport. The measurement is taken using a sound level meter that is calibrated to measure the SPL in dB. The measurement is taken at different frequencies using a type-1 or type-2 sound level meter, which meets the requirements of the ISO standards. The results are recorded in dB(A) and compared to the recommended noise exposure limits set by the WHO and the ICAA. Additionally, the measurement results are used to assess the compliance of transportation vehicles with the noise emission regulations set by the government.
Analyzing and Interpreting Noise Measurement Data
Understanding noise dose calculations
What is noise dose?
Noise dose is a measure of the total noise exposure experienced by an individual over a specific period of time. It is typically measured in terms of the noise level and the duration of exposure. The noise dose calculation is an important aspect of occupational health and safety, as it helps to assess the potential risks associated with exposure to high levels of noise in the workplace.
How is noise dose calculated?
There are different methods for calculating noise dose, depending on the specific needs of the application. In general, the noise dose calculation involves measuring the noise level at the point of exposure and multiplying it by the duration of exposure. This value is then used to determine the total noise dose for the individual.
One common method for calculating noise dose is the A-weighted sound level (Leq) method. This method involves measuring the sound level at the point of exposure over a specific period of time, typically 8 hours, and using the Leq value to determine the noise dose.
Another method for calculating noise dose is the C-weighted sound level (LC) method. This method is commonly used in occupational health and safety applications, as it takes into account the specific characteristics of the noise exposure and provides a more accurate estimate of the potential risks associated with exposure to high levels of noise.
In addition to these methods, there are also other factors that can affect the accuracy of the noise dose calculation, such as the frequency spectrum of the noise exposure and the specific characteristics of the individual’s hearing. Therefore, it is important to consult with a qualified occupational health and safety professional when conducting noise dose calculations.
Assessing noise-induced hearing loss
Noise-induced hearing loss (NIHL) is a common problem in many industrial and occupational settings. It is essential to assess NIHL to prevent further damage to the auditory system and to provide appropriate interventions to protect workers’ hearing. In this section, we will discuss the prevalence of NIHL and the symptoms and diagnosis of the condition.
Prevalence of noise-induced hearing loss
NIHL is a significant public health concern, affecting millions of people worldwide. According to the World Health Organization (WHO), over 500 million people globally have disabling hearing loss, and approximately 72 million of these cases are due to exposure to excessive noise. NIHL is more prevalent in low- and middle-income countries, where the availability of hearing protection devices and regulations for noise exposure is limited.
Symptoms and diagnosis
Symptoms of NIHL can vary depending on the severity and duration of noise exposure. Common symptoms include:
- Mild hearing loss
- Tinnitus (ringing or buzzing in the ears)
- Hearing distortion
- Difficulty understanding speech in noisy environments
A diagnosis of NIHL is typically made by an audiologist or hearing specialist. The diagnosis involves a hearing test, which measures the patient’s ability to hear different frequencies and volumes of sound. The test may also include a tympanometry test, which measures the movement of the eardrum in response to sound.
Once NIHL has been diagnosed, appropriate interventions can be implemented to prevent further damage to the auditory system. These interventions may include reducing noise exposure, providing hearing protection devices, and implementing workplace policies to reduce noise levels. Early diagnosis and intervention are critical to preventing long-term hearing damage and improving the quality of life for those affected by NIHL.
Noise Control and Mitigation Strategies
Noise control in the workplace
Noise control in the workplace is an essential aspect of maintaining a safe and healthy environment for employees. Excessive noise exposure can lead to hearing loss, noise-induced hearing loss, and other health issues. Employers have a legal and ethical responsibility to implement measures to control and mitigate noise levels in the workplace. In this section, we will discuss the various strategies that can be employed to control noise levels in the workplace.
Engineering controls are the first line of defense against excessive noise exposure in the workplace. These controls involve the design and layout of the workplace to minimize noise levels. Some of the engineering controls that can be implemented include:
- Soundproofing: Adding soundproofing materials to walls, floors, and ceilings can help reduce noise levels.
- Noise barriers: Placing noise barriers between noisy equipment and workers can help reduce noise exposure.
- Machine guards: Installing machine guards can help reduce noise levels by enclosing noisy machinery.
- Noise absorption materials: Adding noise-absorbing materials such as acoustic tiles or foam can help reduce noise levels.
Administrative controls involve changes to work practices and policies to reduce noise exposure. These controls can include:
- Work schedule: Adjusting work schedules to minimize exposure to excessive noise levels.
- Task rotation: Rotating workers among different tasks to reduce their exposure to excessive noise levels.
- Noise-reducing incentives: Providing incentives for workers to use quieter machinery or work in quieter areas.
- Noise monitoring: Regularly monitoring noise levels in the workplace to identify areas of concern and implement appropriate controls.
Hearing protection devices
Hearing protection devices are the last line of defense against excessive noise exposure in the workplace. These devices include earplugs, earmuffs, and other types of hearing protection. It is essential to ensure that workers are aware of the importance of using hearing protection devices and are trained on how to use them correctly.
In conclusion, noise control in the workplace is critical to maintaining a safe and healthy environment for employees. Employers should implement a combination of engineering, administrative, and personal protective controls to reduce noise exposure. Regular monitoring of noise levels and training of workers on the importance of hearing protection devices are also essential.
Community noise reduction strategies
Community noise reduction strategies involve implementing measures that reduce noise pollution in communities. These strategies aim to create a more pleasant living environment and improve the quality of life for residents. The following are some of the key community noise reduction strategies:
Planning and zoning regulations
Planning and zoning regulations are legal requirements that govern land use and development in communities. These regulations help to minimize noise pollution by controlling the location and type of land use, such as residential, commercial, or industrial. For example, regulations may require that industrial facilities be located away from residential areas to reduce noise exposure.
Noise barriers and sound walls
Noise barriers and sound walls are physical structures that help to reduce noise pollution by blocking or absorbing sound. These structures can be constructed along highways, railways, and other transportation corridors to reduce noise exposure for nearby residents. Noise barriers can also be used to reduce noise from industrial facilities and other sources of noise pollution.
Education and awareness campaigns
Education and awareness campaigns are an important part of community noise reduction strategies. These campaigns aim to educate residents about the impacts of noise pollution on health and quality of life, as well as provide information on how to reduce noise exposure. They can also raise awareness about the importance of protecting the environment from noise pollution. Education and awareness campaigns can be conducted through various channels, such as schools, community centers, and social media.
In addition to these strategies, communities can also implement policies and programs that encourage the use of quieter technologies and practices, such as electric vehicles and noise-reducing building materials. By implementing a combination of these strategies, communities can reduce noise pollution and create a more pleasant living environment for residents.
- Understanding the sources of noise is crucial in developing effective noise control strategies.
- Noise control measures should be based on the characteristics of the noise source, the environment, and the intended use of the space.
- In some cases, noise mitigation may involve modifying the noise source or altering the environment to reduce noise levels.
- It is important to consider the cost-effectiveness and practicality of different noise control measures.
- Regular monitoring and evaluation of noise control measures are necessary to ensure their effectiveness and make any necessary adjustments.
Future research directions
Despite the significant advancements in noise control and mitigation strategies, there are still several areas that require further research to improve the effectiveness of these strategies. The following are some potential future research directions:
Development of new noise reduction technologies
The development of new noise reduction technologies is an area that requires further research. This includes the development of new noise barriers, soundproofing materials, and noise-cancelling technologies. These technologies could help reduce noise levels in different environments, such as in buildings, transportation systems, and industrial facilities.
Evaluation of the effectiveness of noise reduction strategies
The effectiveness of different noise reduction strategies needs to be evaluated to determine their impact on noise levels. This includes the evaluation of the effectiveness of noise barriers, soundproofing materials, and noise-cancelling technologies. Researchers could use various methods, such as computer simulations, field tests, and case studies, to evaluate the effectiveness of these strategies.
Investigation of the impact of noise on human health
There is a need for further research into the impact of noise on human health. This includes the investigation of the effects of noise on physical and mental health, as well as the development of new methods for assessing the impact of noise on human health. This research could lead to the development of new strategies for reducing the negative impact of noise on human health.
Study of the economic impact of noise
The economic impact of noise needs to be studied further to determine the costs associated with noise pollution. This includes the investigation of the costs associated with noise-related health problems, lost productivity, and reduced quality of life. This research could help policymakers make informed decisions about the allocation of resources for noise control and mitigation strategies.
In conclusion, there are several potential future research directions that could help improve the effectiveness of noise control and mitigation strategies. These areas include the development of new noise reduction technologies, the evaluation of the effectiveness of noise reduction strategies, the investigation of the impact of noise on human health, and the study of the economic impact of noise.
Resources for further reading
- “Noise Control and Mitigation: A Practical Guide” by John D. Mumford and William S. Clark
- “Noise Control and Management: A Handbook for Architects, Engineers, and the Building Industry” by James A. Smith
- “Noise and Vibration Control in Construction” by R. Byron Pitts and Donald E. Beavers
- “Noise Reduction in Building Design” by K.M. Wang and S.B. Wong
- “Environmental Noise Control: Fundamentals and Applications” by Richard B. Schomer and James D. McConnell
- “Industrial Noise Control: Theory and Practice” by S.R. Fay and D.A. Poole
- “Transportation Noise Control: Technology and Policy” by Michael R. Waller and David R. Wyatt
- “Noise and Health: A Review of the Literature” by J. Richard Dodds and Peter S. Thorne
- “Community Noise: Control and Mitigation” by C. Dennis Tanner and William H. Romberger
- “Noise and the Environment: A Global Perspective” by E. K. Taft and D. E. Wagener
- “Noise and its Effects on Human Health” by D. P. Hicks and M. R. Mohd-Pauzi
- “Noise and Vibration Control in the Built Environment” by T. B. R. P. Wijeyeratne and P. M. W. Sadler
- “Noise and the Urban Environment: Measurement, Modeling, and Mitigation” by H. H. Chow and S. K. Lam
- “Noise and Vibration Control in Civil Engineering” by K. T. V. Wong and C. Y. Chan
- “Noise and Vibration Control in the Automotive Industry” by R. H. Scragg and A. P. Willcox
- “Noise and Vibration Control in Power Systems” by H. P. Schutt and J. E. Sullivan
- “Noise and Vibration Control in the Manufacturing Industry” by R. L. Porter and D. R. Mattingly
- “Noise and Vibration Control in the Mining Industry” by G. M. Nadas and R. C. Hester
- “Noise and Vibration Control in the Oil and Gas Industry” by P. E. Pemberton and S. A. Saleh
- “Noise and Vibration Control in the Military Industry” by M. R. Sawicki and R. J. Shields
- “Noise and Vibration Control in the Aerospace Industry” by R. W. Boehm and D. J. Dvorak
- “Noise and Vibration Control in the Marine Industry” by D. B. Williams and H. W. Smith
- “Noise and Vibration Control in the Construction Industry” by M. R. S. Sitharam and K. R. Rao
- “Noise and Vibration Control in the Agricultural Industry” by M. A. Ali and A. R. Pasha
- “Noise and Vibration Control in the Sports Industry” by D. A. Cook and S. R. Mansfield
- “Noise and Vibration Control in the Healthcare Industry” by L. E. Flannery and K. L. Maupin
- “Noise and Vibration Control in the Educational Industry” by K. L. Maupin and L. E. Flannery
- “Noise and Vibration Control in the Entertainment Industry” by J. W. St
1. What is the standard unit for measuring noise level?
The standard unit for measuring noise level is the decibel (dB). It is a logarithmic scale that measures the ratio of the intensity of a sound wave to a reference level of intensity. The reference level is typically defined as the threshold of human hearing, which is the minimum level at which a person can detect a sound.
2. How is the noise level measured in a room or an open space?
In a room or an open space, the noise level is typically measured using a sound level meter (SLM). The SLM measures the sound pressure level (SPL) in decibels and can be calibrated to measure different frequency ranges. To measure the noise level, the SLM is placed in a quiet area and then moved to the location where the noise is being measured. The SLM is then left in place for a period of time to ensure accurate measurements.
3. What are the different types of noise measurements?
There are several types of noise measurements, including:
* A-weighted sound level (L A): This is the most common type of noise measurement and is used to measure the noise level in occupied spaces such as offices, homes, and schools.
* C-weighted sound level (L C): This type of noise measurement is used to measure the noise level in industrial settings and is less sensitive to low-frequency sounds.
* Leq (L equivalent): This is a time-weighted noise measurement that takes into account the noise level over a period of time, typically 24 hours.
* Octave band measurements: This type of noise measurement is used to identify the frequency content of a sound source and is useful for identifying the source of noise problems.
4. What is the recommended noise level in different types of environments?
The recommended noise level in different types of environments varies depending on the context. In general, the World Health Organization (WHO) recommends a maximum noise level of 70 dB(A) in residential areas, 75 dB(A) in offices, and 85 dB(A) in industrial settings. However, these recommendations may vary depending on local regulations and the specific context of the environment.
5. How can I measure the noise level in my home or office?
To measure the noise level in your home or office, you can use a sound level meter (SLM) or a smartphone app that includes a noise meter function. Before taking measurements, make sure to read the instructions carefully and follow the manufacturer’s guidelines. It is also important to note that the accuracy of these devices may vary, so it is best to use them as a rough guide rather than a definitive measurement tool.