By Betta Manufacturing Company, Enfield. Stores ref. 6B/166. Circular white metal instrument. Has rotating discs for setting the ground pressure, temperature, indicated height and airspeed. For use with ICAN calibrated altimeters. Used by Navigators when plotting routes etc. In excellent unused/unissued condition with stores tag, waxed paper wrapping and issue box. Well marked. Stock code M17276.