Re: Triple D'oh! Message #8 Posted by james (UK) on 14 Nov 2003, 4:25 p.m., in response to message #7 by Nelson M. Sicuro (Brazil)
Hi Gang
It's always the little things  reminds me of the hours I spent gazing at FORTRAN listings wondering why the program didn't work and someone would look over my shoulder and point out the ',' that should have been a '.'
My apologies in advance for the formatting  can't work out how to get a superscript 2 for the squares or a sigma sign so please read x2 as xsquared and E as sigma.
The apparent bug results from the fact that the standard deviation function operates on two variables, x and y. Every time you key E+ the calculator accumulates Ex, Ey, Exy, Ex2 and Ey2. When E is keyed the calculator makes the appropriate adjustment to Ex, Ey, Exy, Ex2 and Ey2. If you are only using one variable, the yregister should be cleared first before starting so that y (and Ey, Exy, and Ey2 ) will always be equal to 0. The apparent bug arises when, having called s, which returns both s(x) in the x register and s(y) in the y register, you then enter, in this case, the 4th x (114) which pushes s(x) into the y register and key E then the calculator will in making the appropriate adjustments to Ex, Ey, Exy, Ex2 and Ey2 subtract the square of s(x) from the current Ey2 which was 0 and now becomes s(x)2. When you recalculate s, s(x) can be calculated but s(y) can't be calculated as it now involves trying to take the square root of a negative number and the apprpriate error message is displayed – in the case of the 34C, error3. Extract from the 34C handbook “A nonzero number in the yregister during onevariable calculations of s, r, L.R. may result in a display of Error3”.
s(y) = square root of {[n Ey2  ( Ey )2]/n(n1)}.
With my 12C, 34C and 41CV there is no error display provided that I am careful to ensure that after getting s(x) I key 0 [ENTER] before keying the 4th x (114) and E.
I'm now off to try and make peace with my HPs for ever doubting them!
Best
James
