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

[robert zellmer]

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, 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 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