Is the accuracy interval the tolerance for the instrument?

Does the precision interval indicate a single standard deviation? And more importantly, does the precision assume a perfect operator (so the variance is due simply to randomness) or does it take into account an operators reading/technique?

The reason I ask is because I did a bunch of measurement using a 1 mL micropipette with a "precision" of 0.002 mL and got a standard deviation of 0.0026 and am curious if that additional 0.0006 error is because of my poor technique compounding upon the instruments "inherent" uncertainty.

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    $\begingroup$ I'm not familiar with this type of instrument, but I was taught that for all measurement systems "precision" is how tiny a reading can be made (how fine the graduations are) and "accuracy" is how close a reading is to The Truth. (For example, cheap room temperature monitors which give readings to 0.1 degree C, but in fact their accuracy is much worse than that. Or a simple glass burette where the readings are etched in perfect linear fashion, but the glass bore may vary slightly with length leading to inaccuracy.) $\endgroup$
    – Andy
    Oct 7, 2016 at 7:44

1 Answer 1


Precision and Accuracy are independent. As Andy has stated, accuracy refers to the ability of the device to measure as close to the absolute value as possible, whereas, precision refers to the closeness of the values in repeated measurements. Precision depends on repeatability and reproducibility of both the device and the measurers, assuming all other conditions remain the same (environmental conditions, etc).

Also, you should check how the manufacturer is defining the precision and accuracy. Typically, accuracy or trueness is the tolerance. Precision, may actually be expressed as the Precision/Tolerance ratio, so it is important in determining how you are arriving at your own capability. I would think that what you are after, is either a calibration of your device, or your own reproducibility and repeatability, rather than your precision.

Your particular numbers confuse me. How did you calculate your Standard Deviation? I am a bit thrown off, because I am tempted to interpret your mean as 0.002 and your SD as 0.0006. Please clarify. Here is some guidance on pipette accuracy determination:



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