Looking for advice on constitometer measurement

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#1 egriff4

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Posted 02 December 2016 - 04:02 PM

My company uses a consistometer that measures in marks of half.  We however measure in quarter marks, even tho the quarter marks are not physically marked.  Is this going to to be a problem on an SQF audit? We do not use viscosity as a CCP.  A new employee said we have to measure in half marks but we have been doing in quarter marks for years. Thanks in advance.

#2 egriff4

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Posted 02 December 2016 - 04:40 PM

Consistometer** Sorry, my proofreading is terrible today.

#3 BrummyJim

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Posted 02 December 2016 - 04:48 PM

Hi egriff4,

I would say that without the physical marks it will be difficult to justify (or even demonstrate) your quarter readings. All you can state is that the reading is between half and whole values. You certainly can't state that it is x.25 or x.75 as there's no way you can read to 2 decimal places like that. You might just be able to argue for 1/4 or 3/4.

#4 Charles.C

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Posted 04 December 2016 - 03:12 AM

Hi egriff,

It relates to (intuitive) precision.

See this link for an extended discussion -

http://www.bellevuec...ncert-estimate/

General rule of thumb: It is not uncommon when making a single measurement to avoid all this painstaking process and simple assign one half the smallest scale division as the uncertainty. For instance, the smallest scale division of common pan balances is 0.1 g. In this case we would assume an uncertainty of +/- 0.05 g

Accordingly, a (neutral/slightly pessimistic[?]) option could be to assert that a stated measurement of  X units  is interpreted to mean X +/- 0.25 (units), eg 1.25 = 1.25 +/- 0.25

Of course, whether such a measurement is in fact precise enough to be useful is a different question.

PS - some terminologies in above link are maybe used rather "loosely", eg precision / accuracy are statistically 2 rather different "things".

Kind Regards,

Charles.C

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