The DC 504 Counter/Timer measures frequency from 0.1 Hz (0 Hz with 0.1 Hz resolution) to at least 80 MHz. It measures period from 1"s to 999.99 s, and totalizes events from 0 to 99,999 at a maximum rate of at least 80 MHz. A resolution of 0.1 Hz can be obtained by allowing the more significant figures of the counter to overflow. Five 7-segment light-emitting diodes (LED) provide a highly visible numerical display. The decimal point is automatically positioned and leading zeros (to the left of the most significant digit or decimal point) are blanked. Digit overflow is indicated by a front-panel LED. Signals to be counted or timed can be applied to either a front-panel bnc connector or to the rear interface connector. The DC 504 is designed to operate in any of the TM 500-Series Power Modules. It is completely compatible with other members of the TM 500 family in terms of signal interconnections. The DC 504 is designed to operate in ambient temperatures between 0°Cand +50° C. It can be stored in temperatures ranging from -40°Cto 4-75° C. After storage in temperatures outside the specified operating temperatures, allow the DC 504 to return to a room ambient temperature within the operating range before applying power.