Lufkin-Worlds Inc. "Biggie Munn" Grid Rule

This is one of my most "cryptic" slide rules in my collection, because there are no references about how this rule have to be used. Fabricated in the United States possible in the late 1950"s by Lufkin-Worlds Inc., as a special order for the legendary Michigan State University football coach Clarence "Biggie" Munn (1).  This limited production rule was not accompanied with any brochure, manual or leaflet, and even Lufkin-Worlds did not keep reference of this work, so is difficult to precisely state even the fabrication year.

Is logical to think that Coach Munn had a very clear idea of how to use this rule, but he never left any reference about this.  However, through the manipulation of this rule is possible to infer how Coach Munn could use it. The scales on this rule are not logarithmic, but linear, divided in 100 equal parts. We know that logarithmic scales are used  to multiply and divide, but linear can be only be used to add and subtract.  Because in Football is important to plan the next move according with the yards won or lost in the previous,  this rule had to be used to determine distances.

Two of the three scales on this rule, the outer ones, are identical, divided in 100 parts, but labeled in reverse order respect the other one,  their divisions are labeled from 1 to 99,  and these scales are identified with arrows labeled DIRECTION OF PLAY,  pointing toward the 100 value. These scales have to represent the yards every team has to advance towards goal, and they are complementary, this is, the opposite numbers on the scales add up 100. So if your team is in yard 23, and you read 23 on one of the scales, the opposite number on the other scale is 77  (100 - 23), the distance to goal. 

The central movable scale resembles the yards division on the football field. It is also divided in 100 equal parts, and the divisions are labeled in the increasing-decreasing order 0-to-50-to-0. 

How does this rule work? Well, according with my personal use, in a very simple way. Assume your team receives the kick off, and advancing to the right reaches yard 27. With the rule's in the "three numbers 50 aligned" position, pull the slider the left until the rule's left edge be aligned with "left" number  27 on the slider. The slider's right edge will be aligned with number 73 on the lower scale, indicating the number of yards to goal. (See pictures below)

The rule is giving now all the possible yards to advance on the field yards for the next play. For example, to reach yard 38 on the first half of the field, 11 yards have to be advanced, and this number can be read on the lower scale. If a play reaches yard 38 on the second half of the field, 35 yards advanced can be read on the lower scale, and directly above on the upper scale the yards to goal; 65. (See picture above). The rule can be set up again to a new position and distance readings can be done. 

There are very few references about this rule. I have found a couple only, one in the Oughtred Society  Collerctors Gallery (3), and other in the Worthpoint Corporation website, a site dedicated to determine the value of antiques (4).

References:

(1).  Wikipedia: Clarence Munn: https://en.wikipedia.org/wiki/Clarence_Munn

(2). Holland, Gerald:  A MAN AFTER HIS OWN HEART. Sports Illustrated, November  19, 1962. https://vault.si.com/vault/1962/11/19/a-man-after-his-own-heart.

(3). The Oughread Society. Archive of Collections.  The  Cliff Frohlich Collection.  https://osgalleries.org/collectors/frohlich/info_and_image.cgi?string1=favorites&string2=19206 

(4). Worthpoint. VINTAGE BIGGIE MUNN LUFKIN SLIDE RULE GRID RULE MSU FOOTBALL COACH 1940'S 50'S. https://www.worthpoint.com/worthopedia/vintage-biggie-munn-lufkin-slide-rule-1887969643