Keufell & Esser Morrison Radio 4138

The K&E 4138 Morrison Radio Engineers dual rule was manufactured in the United States in 1939. Designed in the Bell Telephone Laboratories Inc. by John F. Morrison in 1938 with the purpose to help engineers in the solution of radio waves transmission on plane earth surface problems. This rule was fabricated from Mahogany wood covered with white celluloid where scales were engraved, with a glass cursor screwed to plastic ends with metallic frames, and hold with brass braces.

On the front side of the rule there are 10 scales: nine standard and one specialized: L, F, A, [ B, CI, C ], D, T, ST, S, where the scale F is a folded scale labeled FREQ. at the right end, scale that facilitates the solution of LC circuits given a frequency. Nine specialized scales on the back side labeled at their left with numbers: 9, 8, [ 7, 6, 5, 4 ] 3, 2, 1, and at the right with labels indicating the corresponding purpose, were designed to solve field intensity for wide distances, frequency, power and soil conductivity problems.

The Morrison 4138 was only included in the 1939 K&E Catalog, There is no other information specifying in what years other than 1939 this rule was fabricated. This rare rule is one of the jewels of my collection. Rule and leather case are in excellent conditions, much better than the specimen included in the excellent collection www.mccoys-kecatalogs.com, as you can see in the pictures below:

With the scales on front side, and skilled user is able to solve the next problems with two-three decimals precision:

The use of the specialized scales is explained in the User Manual