# Simplified Uncertainty Equation for Pipette Calibration

J

#### jatmoko

According to ISO 8655-6 Annex B, we can use a simplified equation to assess the uncertainty u of the delivered volume at the 95 % confidence level:
u = Es + 2Sr.

My question: What is the volume range we can use for the equation?
Or for what's the volume range (small volumes) we must provide for a complete evaluation, given in ISO 20461.

Thanks.

Last edited by a moderator:

Staff member
From the same annex:

If a more detailed consideration is necessary, e.g. for very small volumes or for delivering apparatus with very high precision, this simplification is no longer valid, and a complete evaluation of the combined uncertainty has to be made.
My opinion.... I would consider all contributors to uncertainty for all ranges, until you can establish evidence of stable values among the different ranges.

Too... you have the issue of how many samples you are taking too.

Have you already completed full analysis on all ranges?​

J

#### jatmoko

I agree with your opinion, It's better to calculate all contibutor.
We just started to arrange a SOP for pipette calibration and study the standart. And wanna to know the limitation the simplified equation. We think with simplified equation = simple work -).

We have not completed full analysis on all ranges yet. I suppose we should do it,If there isnt excact limit for the range,

G

#### George Weiss

Keeping it simple is a lean business approach.
Are you calibrating for your self or a customer?
Is the calibration under ISO-17025 or 13485, ANSI/NCSL Z540.3, and etc. ?
Is your customer in the USA FDA kingdom?
Pipettes are used in regulated medical testing.
Keeping it overly simple can be a non-conformance, and cause serious headaches.
In the calibration of a Pipette, the uncertainty calculations should to be performed in an accepted manner.
This allows for an internationally accepted manner of reporting, to include coverage factor, degrees of freedom, and etc.
Simple is the first step.
Doing it correctly is the best , and final step.

Staff member

I agree with your opinion, It's better to calculate all contributors.
We just started to arrange a SOP for pipette calibration and study the standard. And wanna to know the limitation the simplified equation. We think with simplified equation = simple work -).

We have not completed full analysis on all ranges yet. I suppose we should do it, If there isn't exact limit for the range.
I agree with your opinion, It's better to calculate all contributors.
Especially starting out, it's especially important.

We just started to arrange a SOP for pipette calibration and study the standard. And wanna to know the limitation the simplified equation. We think with simplified equation = simple work -).
I tend to agree with you in philosophy and approach. Too... there is nothing that dictates you need to have some overly complex method of calculating uncertainty. However, all contributors (or potential contributors) do need to be examined.

Once you have done estimations for a while and you have established some stability and such, you can probably look to abbreviate things then.

We have not completed full analysis on all ranges yet. I suppose we should do it, If there isn't exact limit for the range.
I would certainly test pipettes in as many different ranges as you think you can handle. The more the better. It will allow you to have more comparison and perspective starting off. Again, once you have established some stability and process control, you can back off the level of testing somewhat.

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