06-22-2000, 04:28 PM
Unlisted in the Pickett slide rules is the Model 520-T, also known as the US Air Force Aerial Photo Slide Rule Type A-1. Its functions included A, L, DG, FC, C/F, T, S, C, D D/ & K., but more importantly was the reverse which had gradientscales for image sizes in centimeters and feet, ground size in feet, ground speed in either mph or knots, cycling time and overlap features as well as altitude and focal length gradients. I had a lot of use of this one and it still sees some use - if only to see If I can still perform the functions.