Crichlow anti-aircraft circular slide rule army artillery 1943 USA

This is an issued second world war era, large military slide rule. It was developed in 1940 by Robert Crichlow and refused in 1943. The exact workings can be found in the War department field manuals of the era (not included). It was developed specifically for trigonometry for anti-aircraft artillery for the US army and used since. This one was made by the Sillcocks-Miller Company and has military designation B174703 and issued with serial number 2663 which can also be found on the original canvas pouch. It shows only small signs of normal use and age. It is very sturdily build and pretty large. The diameter is ca. 30 cm or 12 inches in diameter. Slide rule, cursors and pouch are in very good condition.  Check the attached video on how to work your vintage man tool : slide rule operation instructions! More background information and the manual can be found here.