I really can't remember taking a formal class on how to use a slid rule. I purchased mine in 1956 when calculators probably did not exist. It is probably still around somewhere. One aspect that seems absolutely critical, at least in my opinion, is that when a slide rule is being used, it forces the ability to at least estimate the answer since the slide rule only provides the first 3 digits in the answer, NOT where the decimal point is located. After using the slide rule for a while, I noticed that everyone who used this calculation aid developed the ability to estimate the answer, almost without thinking about how it was done. let alone why it was essential. As a consequence, it became possible, or so it seemed, to pull answers out of a hat that were often quite accurate, often within about 20%. Many individuals could look at a problem and provide what seemed like a guess even though it was just providing an estimate of a slide rule calculation for which, of course, an estimated answer was essential in the first place. Using a calculator robs the individual of the ability to estimate an answer since the decimal point is provided along with the mandatory digits. Using a calculator also seems to encourage an individual to fail to understand that the input data usually has far too little accuracy to justify more than about two digits of accuracy in the final answer. When values accurate to 8 digits always appear as the result, it becomes very easy to forget that the initial data was often accurate to less than 1%. Further, even when the initial data is very accurate, the equations used to provide a solution can often be VERY non-linear. It is possible to produce variations in the result of more than 50% due to variations in the input of much less than 1%, especially when non-linear differential equations are being used. Of course, doing those kind of calculations even with a calculator would take months or years as opposed to what a computer can do. But the same sort of concept applies as to the accuracy of the result with a calculator. Jerome Fine

On Sun, 3 Mar 2013, Rick Bensene wrote: Not ALL school activities forbade calculators. More than half a century ago, I attended my father's Saturday lecture class on Probability and Statistics. At the conclusion of each lecture, I spent a few hours in "the lab" helping his students with the 100 key calculators. Doing things such as calculating the odds on Craps. In exchange for that work, I was given a few hours access to the stacks of the university library. In my day, slide rules were it. As I mentioned previously, when I was in high school, the SAT and other standardized tests prohibited slide rules (and nobody that I knew had a Kurta), but they ENCOURAGED bringing in scrap paper, including graph paper! AFter my generation folded log graph paper to make impromptu slide rules, they changed the rules. In 1969-1970, in college, I had access to a Wang desktop calculator with nixie tubes, and even a clamshell reader for port-a-punch cards. In 1970 - 1972, at GSFC, in addition to APL, FORTRAN, etc., we had a desktop calculator with a tiny CRT that we rolled around on a typewriter cart. The first time that I saw a handheld calculator (HP) was in 1972. They were ~$350 Then, at my next job, my boss got a 4 function pocket calculator listed me on contract bids as "Manager of Computing Resources" But prices came down! In the mid 1970s, I had calculators, and kept buying more as the prices fell. I remember the FIRST <$5 Commodore! calculator. -- Grumpy Ol' Fred cisin at xenosoft.com

I should have read your reply before making essentially the same point myself. This is a classic case of GIGO, of course. One problem with calculators (and HP RPL machines are worse than most in this becuase they will produce complex numbers, not errors, if you take the sqrt of a negative number or arcsin(2) or..) is that in general no matter what you put in you get _an_ answer. It may be incorrect, but there are digits on the display. Doing an order-of-magnitude estimate first will at least let you see if the anser is reasonable. Indeed. Als, some equations may be mathematically correct but be totally unsuitable for machine calculation. The well-know formula for findign the roots of a quadratic equation can have problems if 4*a*c is small compared to b^2. You end up subtracing 2 nearly equal numbers. The work-around is well-known and quite obvious if you think about it, but an awful lot of people don't think about it. -tony

Another great advantage of slide rules (educationally) is tht they give the mantissa and not the ecxpnent. In other words the user genrally has to do an order-of-magnitude estimate to be able to correctly interpret the slide rule result (there are rules for doing it by rote, but it is easier to do the OOM estimate IMHO). Being able to do such an estiamte is a very useful skill and avoids sillies like the 'genius' who told be the period of a swiming pendulum was a few nanoseconds (!) -tony