what to do with s.f. and rounding in a series of calculations

[Zellmer, Robert]

I believe I mentioned this in lecture but I've received a few questions about it after lecture this

week and in e-mails over the last couple of days.



When doing a series of calculations you should keep track of the s.f. in each step but carry extra

digits to the next step.  How many extra?  At least one.  I usually use several and store the number

(with lots of extra digits in my calculator's memory registers - which you all know how to use after

having your romantic weekend with your calculator).  In lecture I often carry several extra digits

and underline the last significant digit.



On a quiz, you should carry extra digits and round the final answer.  Doing this prevents what we

call "round-off" error.



For lab reports, in the sample calculations you determine a number for a step, including extra digits.

Then write it with the correct number of s.f. (and units of course).  If the number is required on the

report form (or for anything else in the report) you record it there with the correct s.f.  If you need to

use the number in a subsequent calculation you should use the un-rounded number (with the extra digits).



Hopefully this makes sense.



Dr. Zellmer
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