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Mechanical vs digital medical weighing scales: Who wins?

Mechanical vs digital medical scales: Who wins?

Digital or mechanical?

It’s fair to say that digital medical scales dominate the medical world - however, away from hospitals, you don’t have to look too far to find a mechanical (or analogue) scale being used.

In particular, we’re talking about GP surgeries, where - despite weighing equipment still needing to be medically approved, non-approved scales are sometimes still used.

Even those that are Class IIII Approved, despite being legal for medical use, are not recommended for use by GP surgeries by the UK Weighing Federation (UKWF), the concern for their use highlighted in the National Legal Metrology Project report in 2015.

Prior to that, the LACORS report of 2008 had found that 40% of medical scales in GP surgeries were Class IIII, and ‘not recommended for medical use.’

We’ll get onto Class III versus Class IIII accuracy in a moment. But for now, the reason for this blog post. Marsden's M-550 Floor Scale is aimed specifically at GP surgeries. The M-550 is Class III Approved, and because of its low price, we can now make a direct comparison between a digital medical scale and a mechanical medical scale.

The scale we are comparing the M-550 to is a Class IIII Approved floor scale that is most commonly found in GP surgeries, has a similar capacity and is available for a similar price.

So - mechanical scales versus digital scales. Who will win?

Class III Approval and accuracy

As we’ve already mentioned, Class IIII Approved scales can be used in GP surgeries - but are not recommended. Our mechanical scale in this comparison is Class IIII Approved; the M-550 is Class III.

The class approval relates to the accuracy of the weighing scale. So, for example, a Class I Approved weighing scale would be an extremely high accuracy weighing device.

So when can a Class IIII Approved medical scale be used and when should you only use a Class III Approved device?

The Non-automatic Weighing Instruments (NAWI) Directive was made part of UK law in 1992, and under these regulations the scale used for the “determination of mass in the practice of medicine for weighing patients for the purpose of monitoring, diagnosis and medical treatment” must be approved.

The UKWF elaborates on this: “Class IIII scales only have sufficient accuracy for the checking of a patient’s weight for record purposes. Where a weight result is required for monitoring, diagnostic purposes or treatment we recommend that a Class III instrument should be used.”

However, even if Class IIII scales are used, it’s worth bearing in mind the accuracy and whether you’re happy for a less accurate scale to be used even for check weighing a patient.

Specifically, bear in mind that a Class IIII scale, due to its level of accuracy, will probably get away with being less accurate than a Class III scale during testing. During test and calibration of medical scales, a margin of error is allowed by the NAWI regulations.

The maximum permissible error depends on the scale’s class and resolution (or division size). The UK regulations and the UKWF’s guidance notes for permissible errors show that this means the Class IIII mechanical scale in our comparison can actually be further out than our Class III M-550, and still be legal.

medical and digital scale accuracy comparison

The table above shows the comparison if both scales were tested at 100kg.

The Marsden M-550, which measures in 200g increments, is only allowed +/- 400g of error, whereas the mechanical scale, measuring in 1kg increments, can be as much as +/- 2kg wrong and still be classed as accurate enough to pass checks. 2kg is a significant difference when patients are being weighed for medical reasons.

The inaccuracy of Class IIII medical scales has led to the UKWF declaring them suitable ‘where a lower level of accuracy is acceptable such as weighing sand or ballast.’

This Nursing Times post underlines the fundamental importance of using accurate weighing scales.


Marsden M-550 Digital Scale: 1
Mechanical medical scale: 0


How reliable are your medical weighing scales? Reliability is a key priority for Marsden - we’ve put thousands of hours into making sure our Class III medical weighing scales are reliable enough for everyday use.

For example, our M-430 Floor Scale is designed as a portable scale that will withstand constant daily use, and being transported from home to home if it’s being used in the community.

It’s for this reason that all Marsden Class III scales have a two year warranty - and there’s the option of a service contract for extra peace of mind.

As the video for the M-550 below shows, weight readings appear instantly, it switches on without hesitation, and weight readings are clear, true and precise.

With mechanical medical scales, the dial could move slightly - the patient has to be absolutely still otherwise there’s no guarantee that what you see on the dial is correct. There’s no Hold function - like on the M-550, which means as soon as the M-550 finds the patient’s true weight, the reading will hold on the display.


Marsden M-550 Digital Scale: 2
Mechanical medical scale: 0


What features does the mechanical scale in this comparison have? A large display? Check. A non-slip surface? Check.

That’s about it.

In contrast, a key basic feature of the M-550 digital scale that GP surgeries will find beneficial over the mechanical scale is the large weighing platform. The mechanical scale has such a small weighing area, larger adults, or those with larger feet will struggle to stand on the scale comfortably!

But the large, non-slip platform of the M-550 means you won’t need to stand behind larger patients to make sure they don’t topple backwards.

Additionally, the large, clear LCD display of the M-550 is clear and easy to read - and the weight reading is therefore easy to take.

Other features of the M-550 digital scale are Tare, Hold - plus BMI, so getting both weight and BMI readings is possible with one, low cost medical scale.


Marsden M-550 Digital Scale: 3
Mechanical medical scale: 0


As we’ve already mentioned, medical weighing scales go thrown a rigorous testing process in order to be given Class III Approved status. This is one of the reasons why Class III Approved medical scales will cost more than their non-approved or Class IIII counterparts.

However, the M-550 is a true exercise in keeping costs down. This scale has been two years in the making - we were determined to make medically-approved weighing scales more accessible.

To that end, we’ve managed to keep the M-550 price as low as £95+VAT, just £6 more than the mechanical alternative.


Marsden M-550 Digital Scale: 3
Mechanical medical scale: 1


So the mechanical scale is cheaper. But, when it’s less accurate, less reliable, has less features and doesn’t have Class III approval - we’d surmise that it’s really a false economy.

The Marsden M-550 wins!

To see the low cost, Class III Approved M-550 Digital GP Floor Scale in action, watch the video below. Or, order the Marsden M-550 here.