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## Disregard limits and sum

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### Disregard limits and sum

Hi,

internally we have a discussion about rounding and sum of impurities.
When we have a disregard limit of 0.3%, and we have some unknown impurites of 0.25%, 0.301% and 0.7%.
Should we round our results before totalling so that 0.301 becomes 0.3 and should be disregarded?

Or is the sum 1.0%?

Best regards

Ace

### Re: Disregard limits and sum

aceto_81 wrote:
When we have a disregard limit of 0.3%, and we have some unknown impurites of 0.25%, 0.301% and 0.7%.

I would say that if your limit of 0.3% is to one significant figure, then each result can only be to one significant figure.

### Re: Disregard limits and sum

aceto_81 wrote:
Hi,

internally we have a discussion about rounding and sum of impurities.
When we have a disregard limit of 0.3%, and we have some unknown impurites of 0.25%, 0.301% and 0.7%.
Should we round our results before totalling so that 0.301 becomes 0.3 and should be disregarded?

Or is the sum 1.0%?

Best regards

Ace

First result what You disregard is 0.24.
0.25, 0.301 not UDL.
Result of sum regards from Your requirements. 1 per cent or 1.0 per cent. Respectively it's 2 or 1.6 per cent.

### Re: Disregard limits and sum

You need to document whether your limits are inclusive or exclusive. If 0.3 is the limit, is a peak of 0.3 excluded (just) or included (just)?

The motivation for excluding tiny peaks is a historical feeling, dating back to the days of wobbly baselines, that it's wrong to reject something based on the sum of a large number of very tiny bumps, which might just be noise. This is a good justification, but it was never intended as a justification for ignoring definite contaminants.

If your motivation for worrying about the extra 0.3% is that 1% summed contaminants is the threshold at which disaster strikes, then the answer to the rounding question is this:

If you have only three, well-defined contaminant peaks that sum to 1.25% of the total, are you excited about the idea of explaining to a regulatory body why 1.25% < 1.0% based on what might easily look like creative use of rounding?

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