Graphical Firing Table M17 Slide Rule

This one-sided rule is made of two types of wood and painted white on top. The top edge is beveled and has a scale for 1:20,000 yards. The top of the base has scales for 100-yard shift, 33 1/3 yards, and range, with D and K scales at the bottom. The D scale is a standard logarithmic scale for multiplication, but the K scale is not a logarithmic scale for cubes. The bottom of the base is marked: GRAPHICAL FIRING TABLE. The top right corner is marked: B180971. The bottom right corner is marked: B180972. The clear plastic indicator has white plastic edges. A black wheel is inside the bottom edge of the rule.

Originally the instrument would have had three slides, including one with a standard logarithmic C scale, but this example has only one slide. The slide was used to position an 8-inch M1-type howitzer armed with high explosive M106 shells, M51 and M67 fuses, and charges of 5, 6, or 7. The howitzer was a U.S. Army cannon introduced around 1942 and used into the 1950s. One side of the slide is for setting the cannon at a high angle and has scales labeled ELEV., 10 M Si (change in elevation), DRIFT, and TF (time of flight). The other side is for setting the cannon to fire at long range and has scales labeled ELEV., c, DRIFT, and FS (fuse setting). The left end is marked: LONG RANGE (/) FT 8-J-1. This mark indicates the corresponding firing table. The right end is marked: GFT M17 (/) C81758.

The back has tables for accounting for the influence of changes in temperature and wind direction. A third table provides range limits for charges from 1 to 7. The right end is marked: TABLE, GRAPHICAL FIRING, (/) M17 (/) STOCK NO. 6574317 (/) 81873. A dark brown leather case has a belt loop and a strap for tying it to the leg. Two additional vertical pockets inside the case held the additional two slides. The flap is marked: CASE, CARRYING (/) M23 (/) D4130. Clark McCoy attributed the rule to Keuffel & Esser, a prominent New York slide rule manufacturer. For another graphical firing table, see 1977.1141.25. One use for the ENIAC and other early electronic digital computers was to compute artillery firing tables.

This example of the firing table was owned by Willard H. Eller (1892-1974), who chaired the physics department at the University of Hawaii from 1931 until 1957.

References: Dr. Ing. Federico Ramirez Santa-Pau, "The Artillery Graphical Firing Table: A Description of a Specialized Slide Rule," Journal of the Oughtred Society 9, no. 2 (2000): 17–20; Clark McCoy, "Graphical Firing Table Slide Rule," http://www.mccoys-kecatalogs.com/KECollection/GraphicalFiring/K&E_GF_1.htm.

Robert M. Kamins and Robert E. Potter, Malamalama: A History of the University of Hawaii, Honolulu: University of Hawaii Press, 1998.

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