Slide Rules

Hoping that new ideas will come with new decor, I have started to renovate my work room, it was neither tidy or untidy, it’s just where I work.  Like most other people, I have gathered together a small personal museum, how I came to possess an empty bottle which once contained a laxative mixture will remain a mystery.  Most of the other stuff has some relevance, fortunately, there is not too much of it, so I can write a few notes about it without losing too much of my life.

I have two slide rules, one belonged to my grandfather who was presented with it on leaving the Croydon Electricity works in 1902 and mine.  I remember purchasing mine in 1973 when I enrolled on an OND course in engineering.  It came from a shop in Chatham which supported the local  draughtsmen and related trades, the last time I passed it it was a tattoo parlour.  The slide rule is a British Thornton double sided engineering model.

Sadly, my grandfather’s slide rule is no longer functional, the slide is stuck and the cursor broken, hopefully it may loosen up now it is on display in a cabinet.  I did manage to do some simple multiplication on mine, but it will take a little time to remember how to use all its functionality.  It, not me, is capable of sin, cos and tan calculations and those in involving natural logs and exponentials and maybe some others which I never mastered.

From what I remember, slide ruling was a competitive activity at college.  If you were really good, you could hold the rule in one hand and move the slide by tilting it either to the left or right, then applying a final adjustment without laying down your pencil.

Now that computing capacity is universally available, it’s hard to remember that for a couple of centuries, that calculations were effectively manual labour.  The early haversine tables used by navigators were compiled by apprentices on a sailing vessel, there must have been an element of compulsion or reward because that would not have been a fun job.  At the turn of the century, heavy statistical calculations were done with pencil and paper.  I have vague memories of being taught to do sums efficiently, today you just use a computer with adequate precision and rarely think about making the machine’s task lighter.

In the 1930’s major computing tasks were sometimes performed by room fulls of people working on mechanical calculators.  These machines occasionally turn up at car boot sales.  When I was an apprentice in an engineering company, a few of these machines were lying around, but numerical tasks had migrated to early electronic computers which took their input from punched cards and presented their output on line printers.  For some unknown reason one was not allowed to punch one’s own cards, this had to be done by what was effectively a typing pool.  One quickly learnt that politeness was at least as important as coding skills in getting a job done.  A card punch operator could correct some of your errors, people who complained a lot seemed to have a lot more bugs in their code.  One person did try and format cards and output in such a way that the card reader and line printers became musical instruments, nobody seemed very impressed.

Programmable calculators such as the HP45 were quite common at the time, whilst these devices were undeniably powerful for their size, for me, Fortran and Dartmouth Basic were a better option. I was probably too lazy or not clever enough to get my head around Reverse Polish Notation.

At the end of the 1970’s spreadsheets such as Lotus 1-2-3 were coming into general use and became much loved by economists.  Whilst these were handy for sums, the early versions had limited abilities for processes like iteration and modelling.  Today’s version of Excel has some really powerful add-ins, one which I like is “Solver” which allows techniques which would otherwise require some complicated coding.


About SolarBucket

I trained as a mechanical engineer in the 1970's and then spent most of the following 25 years doing sums and software for Oil and Gas Exploration. Current interests are the study of wind and solar resources.
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