A 10 mL graduated cylinder has calibration marks representing each mL and 0.1 mL. Accurate readings should be estimated and recorded to the nearest:
a) 1.0 mL
b) 0.1 mL
c) 0.01 mL
d) 0.001 mL
My instinct says c) 0.01 because you are supposed to have one estimated digit after the 0.1 (or are estimated digits only used in the sig fig rules for "calculations" and not for "measurements"?) My chem lab teacher just confused me more when I asked for clarification.
He said for the centigram balance scale we write to the 0.01 (which does not include an estimated digit) and for the milligram digital scale we write exactly what is shown on the screen, to the 0.001 (which also does not include an estimated digit).
So when do we include an estimated digit, and when do we not include an estimated digit?
Answers & Comments
Verified answer
It has to depend upon the instrument you are using, the spacing of the finest divisions on whatever scale you are reading, and, in the last analysis, on common sense.
I obviously don't know exactly what your graduated cylinder looks like, but I doubt that you could read a liquid meniscus to an accuracy of one-tenth of a division. Stick to the marked divisions, that is, to the nearest 0.1 mL. Common sense rules, OK ?
You confirm this with your example of the balance scales. Again, I don't know what sort of scale you are referring to, but presumably the scale divisions are too close together to make it feasible (or sensible) to estimate to a lower level than the smallest scale division - common sense again !
And for a digital scale, obviously there is absolutely no way that you can know whether a figure shown on the screen is an "exact" value, or slightly under, or slightly over, so you have no alternative to accepting the figure shown just as it is. Common sense - common sense - - COMMON SENSE !