Special Slide Rules and Calculators

Meteorological Office Pilot-Balloon Slide Rule Mk 5

This slide rule or computer is used for calculating the upper wind speed from the resulting angles and distances obtained from tracking a pilot-balloon by theodolite or RADAR.
The original Meteorological Office pilot-balloon slide rules were introduced in 1915. The Mk5 shown here was introduced in 1968 - or so I am deducing from the 4015/68 marking on the bottom right-hand-side of the rule.

Length End-to-end 24.5 inches. Width 2.5 inches.
This rule comes in a fitted wooden box.

Manufactured by Blundell Harling Ltd of Weymouth UK