# Can linearity be used as a substitute of accuracy

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#### I_know_nothing

Hi all,
Is it necessary that an Instrument have accuracy mentioned in its specs? Can linearity act as a substitute to explain the accuracy of an instrument?

Suppose, I have an instrument. I calibrate it using a standard reference between Zero and Span. Now if the instrument has a linearity of 0.1% then for all intermediate values, the readings are likely to be within 0.1% of the line joining Zero and Span. Isnt it, then, enuf to NOT worry about the accuracy? How will the information about accuracy be any different from Linearity, in such a case.

I am sorry to ask such a basic question but I am stuck up with an instrument where I have to know its accuracy. The spec sheet mentions everything BUT the accuracy. It talks about Zero drifts, span drifts, minimum detectable limits, noise, linearity etc.. But not accuracy. So I am trying to understand, if accuracy is at all required to be known for an instrument OR linearity information should suffice.

Regards

#### David_2

Have you contacted the instrument's manufacturer and asked for an accuracy spec and a source for referencing that value (like a spec sheet)?

FYI, when an accuracy spec is stated it is assumed to be at some "reference conditions", like room temperature (60°F?), atmospheric pressure and within some nominal relative humidity range.

Many instruments provide values for the factors that you cited (drift, repeatability, temperature, noise, hysteresis, etc) so that a working accuracy can be calculated to take into account how those factors affect the accuracy.

Typically there's some mention of hysteresis along with linearity because when the measurement decreases it doesn't always always have the same error from linearity as it does when it increases for a given domain x.

You've calibrated your instrument, so it should be 0.1% between zero and span at the conditions under which you calibrated it. But over time it will drift or it now has an offset or skew depending on how the conditions under which you calibrated it differ from its assumed reference conditions.

> Is it necessary that an Instrument have accuracy mentioned in its specs?
Answer: No, but it is a reasonable expectation.

> Can linearity act as a substitute to explain the accuracy of an instrument?
Answer: It depends on who "audits" you