You can use the old style analog meter to measure duty cycle. Duty cycle is defined at the ratio of "on" time to "off" time. On is defined as when the voltage is high and off time is defined as when the voltage is zero. If the on time is equal to the off time the duty cycle is 50%.
So given that as a basis for discussion one can read duty cycle using an old style meter. Here is how to do it.
It is important to know the voltage level during the "on" and "off" times. Knowing that allows one to make a simple reading and then calculate the duty cycle.
Lets assume that the voltage during the on time is 12v and zero during the off time. When we read a duty cycle voltage the meter will average or integrate the voltage between the on and off times. So if we were at 50% duty cycle then the meter would read 6v or half of the voltage during the on time. If we read 5v then we can calculate the duty cycle to be 41.55%. If we read 4v then we have a duty cycle of 33.33% and so on.
The formula is  duty cycle = Vread * 100 / Von
in our example 41.666 = (5 * 100) / 12
where;
Vread = voltage read my the meter
Von = voltage during the ON time
Hope I have not confused the issue. No need to go buy an expensive meter just to read duty cycle.
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