Greetings…this is long, so please bear with me…

Does anyone out there in MoHPC-land happen to have a copy of an old internal HP document titled (I think) "Error Analysis for the HP-35"??? If so, I would like to get a copy of it - scanned or on paper. And I'm sure the Museum would like a copy too. As I remember, the document covers the accuracy of each mathematical function down to the last decimal place, and shows the results with numerous graphs. This document is probably the basis for the old HP Journal article "Algorithms and Accuracy in the HP-35." [Dave Hicks - BTW, I tried the link to that article and it appears that HP no longer has it available on their web site.]

Here's the background story to my request: about January 1973 (when I was in junior high school) my father's long-awaited HP-35 finally arrived. He was teaching high school chemistry at the time. Because of his math and engineering background, he was interested in how the little beast did its internal calculations. He contacted the local HP rep (they used to have an office here) for information and was rewarded with the document I am asking about. He recently gave me the calculator (no batteries, but still works on AC) and I asked him if he still had the "Error Analysis." He has searched and can't find it. I would like it both for my collection and for a short article I plan to write for my company's internal quality newsletter.

The part that most interests me for my article is the part of the "Error Analysis" that deals with HP's implementation of the "Tests for Reasonableness," which are the simple rules for determining how many decimal places belong in an answer. Thus, for addition and subtraction, the result cannot have more decimal places than the input number with the most decimal places, and for multiplication, the result cannot have more decimal places that the sum of the number of decimal places of the input numbers.

I'll give y'all a hint of what my article will be about because it may save you some grief in using a personal computer for calculations. I won't bore you yet with how I found this (I've bored you enough as it is), but try this in Excel: enter the equation =100-99.99-0.01 into a cell and hit Enter. Instead of ZERO, you should see 5.1156995306556E-15 (if you don't see it, format the cell to General and widen the column). As you can imagine, this can ruin a perfectly good test for ZERO, etc. I have a whole list of similar equations: most produce ZERO, but many don't…shades of the Pentium bug. I have tried this on everything from a 286 on up and in many different software packages, of which only Q&A (the old DOS database) and Word for Windows 1 got the right answer. Q&A had an advantage because it was limited to 7 or 8 decimal places. I even called Mathcad tech support several years ago and asked why they didn't implement the "Tests for Reasonableness" since Intel didn't see fit to do it. I mentioned that HP has been doing it for years. Their recommendation was to use the various rounding functions to fix the problem. I knew that already.

I've done enough damage, so I'll quit now.

Thanks for hanging on.