Made in London by Henry Hughes & Son Ltd. Stores reference 6B/108. Circular white metal instrument. Has rotating discs for setting the ground barometric pressure, temperature, indicated height and airspeed. For use with isothermally calibrated altimeters. Used by Navigators when plotting routes etc. Clear Air Ministy marks. Predates the more commonly found MK.II & IIA. The metal is grubby and one of the discs has minor edge loss - see photographs. Good used condition. Stock code M22952.