Rule Slide MG Mk IV for Vickers machine gun

Aluminium slide rule, Mk IV, with two reversible slide scales. The slide rule is made from a solid green aluminium frame and is clad in light guage aluminium sheeting which contains all the printed and etched information. The Mk IV slide rule provides a writing space as well as providing tangent angles, lift for fifty yards and adjustment figures for air temperature and barometric pressure variations. One edge is marked with a 1:25,000 scale and the other, a one inch equals one mile scale graduated in units of thousands of yards. The safety angle scale, windage and wind speed can be factored into the calculations. The slide rule can also convert metres to yards. Attached to the end of the slide rule is a twenty four inch length of string or graticle cord which has a small ceramic bead attached at one end.

This tool was designed to be used in conjunction with Army issued range tables and was calibrated for use with Mk.VIII (pointed) .303 inch ammunition. This was the final version produced, replacing the MkI wood and MkII duralium versions. In the hands of an experienced officer this sliding rule could replace range tables and speed up calculations. However, in the hands of inexperienced personnel, mistakes could be made. The Mk IV version was in service with the Army from 1940 to 1953 when it was replaced by reissued printed range tables..

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