Scalextric Speed Computer

(9.4" (ō 3") Scale Seconds & Metres scales, C276)

Image Prior to my enlightenment in 2011 I didnít think I had had any real exposure to slide rules, but I now realise I was wrong. In fact many children like me would have been using one in their play in the '70s, '80s and '90s in the form of the Scalextric Speed Computer.

This cardboard device was supplied on its own or with a mechanical lap counter, and is essentially a specialist circular slide rule.

The speed Computer allows the user to determine the scale speed of their cars in KPH or MPH for a measured time (in seconds) over a length of track (in meters).

Construction is two discs of stiff card (c 1/40 inch) held together with a metal rivet. The large bottom disc is 5 inches diameter, the small top disc is 3 inches diameter with a 5/8 inch pointer.

The top disc has a logarithmic METERS scale running anti-clockwise from 15 to 60, with the pointer between the 15 and 60. The bottom disc has logarithmic scales, inside to outside; SECONDS anti-clockwise from 10 to 40, adjacent to the meters scale on the inner disc; KPH clockwise from 97 to 386; MPH clockwise from 60 to 240. The back features a reference of slot lengths in centimetres of common track pieces of the time, to assist in calculating the overall length of track covered.

Use is simple, align the distance covered in meters (usually whole laps) on the top disc with the time taken to cover the distance, in seconds, on the bottom disc, and read the scale speed indicated by the pointer in kph or mph.

The scales are configured clockwise/anti-clockwise since speed is inversely proportional to time, aligned 62.14mph = 100kph = 15m per 17.28s at 1/32 scale for the appropriate conversions and position of the pointer, and scale minimum and maximums chosen for practicality of use (although it can be seen that scale speeds achieved as significantly faster than real-life speeds).

This one is not my original, although that may be hiding somewhere, and they are still readily available second hand.

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Count Belmiro © Copyright June 2012 - July 2015
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