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Balance Acceptability Range


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The acceptability range for our both of our scale balances (200 g and 500 g) when weighed during day of use scale QC is ±5 g. I didn't set this range, and I'm not sure how it was determined, but one of the techs would really like the range readjusted. I agree with them that it's probably best practice to create a more stringent range, but I'm not sure where to start.

The scale we're using only measures in one gram intervals with a maximum range of 1 kg (it's an Ohaus CR2200), so a lot of what I've read about weight range determination will be difficult to implement. It also seems like a good bit of the advice pertains more to weight calibration, which our facilities outsources.

I hope y'all have some insight for me! Maybe I'm overthinking this whole situation.

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I assume that as there are no decimal points involved there is little, if any, variability on day to day readings. Remember the purpose of daily checking the scale is to ensure it is fit for YOUR purpose at the max acceptable ranges in variability, which is why information is harder to find, each lab has to determine what is appropriate for them. Therefore if your inspectors have no problem with the range why would you. An additional advantage of the wide range is that you will/may see a drift in readings if the scale starts to malfunction and so have time to call someone in to fix it before you can no  longer use it.

I personally see no reason to make things harder without good reason or just because you can. 

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So many questions...  :)

Like @John C. Staley said, what is the scale used for?  We have several in our lab.  Some are for weighing whole blood or platelets, some are for making reagents.  Different tolerances could be allowed based on the risk.

What does the manufacturer claim it can perform at?

We do daily QC on our scales.  Four points, 20g, 100g, 200g, and 500g.  We expect the 20 to be +/- 0.1g and the others to be +/- 1g.


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