Hi. This will measure frequency from 10 Hz to 100 kHz, but won't tell you directly what the duty cycle is. The duty cycle is the percentage of time the signal is high out of the total signal. I imagine this meter is measuring the time from one edge, rising or falling, to the next. This is called the period. The frequency is then found by calculating the reciprocal of the period, that is, freq=1/period. If you know that you programmed the PWM for 50% duty cycle, and the meter reads 10 Hertz (it's low end of the frequency range) then the LED should be flashing five times a second. If you THINK you programmed it for 50% and it's actually one percent, you're not going to see any blinking. This meter is not going to help you in this respect - DIRECTLY. However, you can get a running idea if you put the meter in DC Volts range and see what the reading is. If the frequency is less than a 100 Hz (I'm guessing here) then you'll see the AVERAGE voltage of the signal. This should give you an indication of the duty cycle. If the frequency says 10 Hz, for instance, and the Volts reading is 2.5 Volts AT THE PIN driving the LED (NOT THE LED) then it's PROBABLY 50% duty cycle. For this to work, you will want to set the frequency for the LED blink within the range of the meter, and have the meter volts setting at a range just above the chip's Vcc.
Then again, you can just go online and Google for "sound card oscilloscope". There are a few programs out there that will let you use the PC's audio input to the sound card to study small, slow signals. Say, one Volt pk-pk, up to 20 kHz. This should be plenty fast enough for what you want to do. These sites will//should tell you how to step the signal down to a safe level, and how to make a probe to connect between the pin and the audio connector.
And try turning the LED around first on the chance it is in backwards!
Later!
kenjj