Exp 16 pre and post-lab sig fig.

[Robert Zellmer]

I often receive questions about the sig. fig. in exp 16 when it comes
to averaging the f.p. determinations to get the average f.p. which you
report on your sheet and in the on-line data-entry post-lab.

In class we discussed how you can average several numbers and gain sig.
fig. That is correct.  That's why we take lots of measurements and average
them.  However, in practice when dealing with experimental data including
an additional sig. fig. in an average or from a graph really can't safely be
done with only 2 or 3 numbers.

Think about exp 1 in which you were plotting your data. The purpose of
a best-fit line is to average out the random error in your data.  If you had
only 2 pts the line would go through both points and wouldn't have show
any effect of random errors.  Adding one more point wouldn't make it much
better. Having at least 4 data points would make it more plausible to gain a
sig. fig. (both when averaging and from a graph).

When you add up your determinations for the f.p. for each trial adding only
three values isn't enough to give confidence in reporting an extra s.f.  
If you
did five determinations and averaged those I would say you could probably
report 1 extra s.f.  This will certainly not be the case for the 
pre-lab.  Even
for the post-lab you can only enter 3 determinations so don't report an
extra s.f.

I thought this had been addressed in the "Directions" button in the on-line
data input program.  I guess it isn't for the pre-lab.  Keep this in 
mind for
the post-lab input.

Dr. Zellmer
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