Use in a quiet environment. Any ambient noises can affect result accuracy. Complete silence is the best.
Recommended way to record the ticks is to touch the crown of the watch with the headset microphone. You will get the best results using original Apple EarPods.
This is a simple version of Watch Tuner application. Not everyone needs detailed information about a watch movement, sometimes only accuracy is important. Watch Tuner Lite uses very similar algorithm like Watch Tuner does but displays only seconds-per-day deviation.
If you want to know how much your watch is fast or slow, this application is for you.
If you prefer to measure also beat error and amplitude, try Watch Tuner - a bigger brother of this app.
If you need frequency diagram look at Watch Tuner Timegrapher - the most sophisticated app of Watch Tuner series.