To expand on the previous good definition of duty cycle: The period of the event that duty-cycle represents does not have to be any set time-length. The first event to monitor is thus frequency. When asking about the meter, looking for duty-cycle, with salespeople that don't know what about the electronics being tested, frequency is something they usually understand. Frequency tells you how long the event takes. How much of that time is on or off is the duty-cycle. Equipment that measures frequency will usually do duty-cycle.
Bosch Master, ASE Master, L1
33 years MB technician