Operating Instructions for AN/APN-1/A Aircraft Radio Altimeter 1943 A-6 The markings are clear and

The markings are clear and the glass and case are intact

Still not bad for an artifact that is more than 70 yrs old

Here is a student workbook that helped cadets understand the functions of aircraft

Torque Pressure

The fifth section

Operating Instructions for AN/APN-1/A Aircraft Radio Altimeter 1943 A-6 The markings are clear andThis is an original WWII era manual, Handbook of Operating Instructions for AN APN 1 and AN APN 1A Aircraft Radio Altimeter system, dated June 1943. The Radio Altimeter was used in a number of aircraft of the US Army Air Force and US Navy where close monitoring of height over terrain was critical, such as torpedo bomber TBM Avenger (see image from TBM Flight Manual), dive bomber SB2C Helldiver, patrol aircraft PV 1 Ventura, PV 2 Harpoon, PBY Catalina,