Special Slide Rules and Calculators

Meteorological Office Humidity Slide Rule Mk3A

Meteorological Office humidity slide rules are designed to enable the Humidity, Relative humidity, Dew point, Frost point, Vapour pressure and Mixing ratio to be
calculated quickly from psychrometer observations, either screen or aspirated, and either at ground level or in the upper air.
Brief instructions are given on the back.
Date of manufacture Circa 1953
L = 11.3 inches W = 1.75 inches Blundell Rules Ltd. Weymouth. UK.

Showing Front, Reverse of slide and back of rule.