A very nice original WWII US Air Force issue True Airspeed Computer A.C. Type G-1. This one is unissued and complete in its original ussue card packet. The packet has several lables stuck over each other at the top, one having an inspection date of April 1945, so this must have been previously checked in 1942 as they were to be checked every 3 years. These computers were used on bombers during WWII. The computer is in totaly mint untouched condition and the order number begins with 42 (which I believe is the date of manufacture). The card casing is strong and original to the item. It was manufactured by the Cruver Manufacturing Co. from Chicago

How does it work?
Aircraft display an indicated airspeed on an instrument called an airspeed indicator. Indicated airspeed will differ from true airspeed whenever the aircraft is flying in air whose density differs from the density at sea level and 15 degrees Celsius. Air density is affected by temperature, moisture content, and altitude. Indicated airspeed is used in aircraft operation as the aircraft stalling speed and structural limiting speeds are dependent on indicated airspeed, irrespective of true airspeed. However, proper navigation via dead reckoning (without constant ground reference) requires the use of true airspeed and wind corrections.

To measure the true airspeed with this apparatus you had to set the pressure altitude against the calibrated indicated airspeed (M.P.H) than set the indicator on air temperature. You than could read the true airspeed on the scale under the indicator. You could use the notched side of the indicator to mark the air speed meter calibration on the blank arc.