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SunPro duty-cycle meter

Correct me if I am wrong, but the duty-cycle meter measures the percentage of
time that a binary signal is on.  If you know the amplitude of such a signal,
you can use a cheapo analog voltmeter to measure the duty cycle.

the DC voltage that the instrument shows
----------------------------------------  =  duty cycle
    amplitude of the binary signal

This works for low-enough frequencies (all valve-controlling signals are such
because the response time of the meter is faster than the response time of
the valve), and the analog voltmeter basically integrates the binary voltage
giving you the average voltage.

A solid analog voltmeter will run you about $20, and the SunPro that I saw
was closer to $100.

True, it measures RPM, but most cars have an equally good RMP-meter already;
it also measures the dwell angle, but most Audis don't have points anyway.

I had no trouble using the regular (analog) voltmeter to measure the duty
cycle on several occasions.