Re: [Phys-l] Significant figures -- again

[Philip Keller <PKeller@holmdelschools.org>]

> bounces@carnot.physics.buffalo.edu] On Behalf Of Richard L. Bowman
> One should not apply it to intermediate results on the way to a final
> answer. This is also true forr the more formal derivative method. One should
> look at the whole procedure not just at parts of it.

Yes, I agree.  But that is still strange!  If every day, I throw some pennies in a jar, I can keep track of the current total by adding the new amount to the previous day's total.  No one will suggest that to get the right answer I have to re-add the daily contributions.  But if I have that 12000 lb  bus and then over 50 days 50 passengers get on the bus, one each day, then at the end of each day I find that the weight has not changed (according to the rules of sig fig addition). But if I add up the passenger weights first and then add, I get the more reasonable result.  So this time,  I can't just add the mass of the new passenger to the previous running total.