Made in London by Henry Hughes & Son Ltd. Stores reference 6B/131. Circular white metal instrument with rotating discs for setting the ground barometric pressure, temperature, indicated height and airspeed. For use with I.C.A.N calibrated altimeters. Used by Navigators when plotting routes etc. Clear Air Ministy marks and 1939 date code. A bit grubby but in very good used condition. Stock code M23409.