K&E 4091-3 Special Production Slide Rule
This slide rule is an obvious special production run of the 4091-3 with the LC scale added. Karen Miller had this rule from the time she worked worked at a laboratory at China Lake, CA. From the serial number it was probably produced in 1936 to 1937. The significance of this rule is that it is the first known slide rule by K&E to use the LC scale intended for use in electronics calculations. The LC scale was to be later used on the 4139 Cook Radio Slide Rule. The significance of the nomenclature "RMS No. 72" in the last picture is unknown.
Pictures courtesy of Karen Miller and Clark McCoy