The Douglas Sky Rule, a six inch long slide rule device with leather carrying case and original storage box. Includes a 12 page instruction manual and original guarantee certificate with registration form. Gordon Cooper has printed his last name on both the leather case and manual just after receiving the instrument in the 1950’s. With a Typed Letter Signed by Gordon Cooper.

Both the leather carrying case and instruction manual have been SIGNED by GORDON COOPER. Accompanied by GORDON COOPER’S signed provenance letter on this personal stationery which reads: “This Douglas SKY RULE was given to me by Mr. Don Douglas of Douglas Aircraft in the 1950’s while I was an Air Force Officer. I used it during many Air Force and NASA jet aircraft flights. It was a convenient tool to compute air speed, mach number, pressure altitude, and other important flight parameters. I found it to be a very advanced and useful instrument for the period it was used.”