20 inch Faber Castell Slide Rule

Once again I am studying my biology course, so today is not a good day for searching out blips. Having recently posted a picture of one of my mechanical calculators, which are essentially digital, I thought it might be an idea to show an analogue calculator and chose a 20 inch slide rule.

These were used, mainly by engineers, when reasonable precision was required without the inconvenience of log tables or a mechanical calculator. 20 inch slide rules were relatively unusual the most common being a 10 inch, in use in the office or a 5 inch in your breast pocket for use in the field. The greater the length of the rule, the longer the scale and the higher the precision with which results could be read. A 20 inch rule would give accuracies of between one part in 2000 and one part in 5000, if used with great care and was very quick to use. I used slide rules from about 1957 through to the mid 1970's and actually physically wore out three or four during that time, before scientific electronic calculators became commonplace and replaced these. My favourite slide rule, which I wore out and could never replace, was a Faber Castell Mathema, which was designed to work with hyperbolic functions, their integrals and their derivatives; no other slide rule had these capabilities.

The slide rule shown is very basic in that it was only designed for use for multiplication, division and simple powers.