If you hold the middle button on the grip frame till it comes up with the zzzz sign like you are going to turn it off but instead of pressing the middle button again, press the top button and cycle through the menu until you reach the display menu. There you will be able to change between alarm, timer, peak rate and average rate.
I found it better to have it on average as it records the rate over 1 second rather than recording the time between 2 consecutive trigger pulls like peak rate does.
I can only hit 12 bps max without air on the marker, but in training mode with air i have managed to hit 18 bps. Not a constant 18 bps but still got there.