Are Chair Scales Accurate?


A chair scale is a chair with an integrated weighing scale. Depending on the make or model it may be an actual wheelchair or a mobile chair (small wheels to make them easy to move from room to room). They are useful for patients who cannot stand whilst being weighed, making the process quick and easy for the patient and medical staff alike.

A chair scale can be lightweight (easy to move) or more substantial (suitable for bariatric patients), depending on the purpose and setting the chair scale is required for.

When weighing someone in a professional medical setting, for example prescribing medications to patients, the scale must, by law, be Class III approved.

A Class III approval, or verification, will ensure the chair scale is accurate. 


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What is a Class III Approved Scale?


A medical weighing scale which is Class III approved will meet the accuracy standards required for use in a professional medical setting, under the Non-Automatic Weighing Instruments Directive (NAWI Directive).   

Other examples of type of Class III approved scales used in other industries would be retail scales such as supermarket checkout weighing scales, industrial scales and weighbridges.

The Class rating for scales goes from Class IIII (lower accuracy) to Class I (the most accurate scale available).

Class I and Class II approved scales are very highly accurate instruments which are intended for things like weighing precious metals.

A Class IIII scale would be fine for use in a gym, slimming club, nursing home or even a GP consultation room, but is only suitable for checking a patient’s weight for record purposes. If a patient’s weight must be taken for diagnostic or treatment purposes, a Class III scale must be used, by law.


How is a Scale Approved for Class?


For a medical scale to be verified for use as a Class III scale, it must pass a verification test. A verification test, sometimes called stamping, will put the scale through many rigorous procedures, including tests which ensure it will repeatedly display the same and correct weight if a patient steps on and off the scale several times.

A scale can only be approved, or verified, by a person or organisation who has the authority to do so. Once approved, a scale will carry a CE mark and a ‘Green M’ label or in the last two years an M followed by the verification year eg. 'M18', as well as the four-digit number which refers to the organisation responsible for verification.


How Often must a Chair Scale Undergo Calibration?


We have established that a chair scale is indeed accurate for use in a professional medical situation if it has a Class III validation, with a Green M label (older models) or M18 (newer models) and a CE mark.

However, over time scales inevitably lose accuracy due to age, general wear and tear, or occasionally due to circuitry malfunction.

To ensure your chair scale remains accurate after purchase it must be tested for accuracy periodically. 

It is advisable that you employ a company to test your scale(s) at least once a year. This will ensure that the scale remains at the accuracy standard required for its class.


Buying Medical Chair Scales


Your medical scales supplier will be able to confirm that your scale meets the requirements needed for your circumstances. Often, when non-Class III scales are being used it is down to misinformed procurement officers, or simply that the medical professional is unaware that the scale is not suitable for the purpose it is being used for.


Solent Scales provide a range of Class III approved medical scales, including Chair Scales, suitable for professional medical uses. We also offer service contracts to calibrate scales which ensures they remain accurate year after year. For more information contact our knowledge team today.

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