The actual frequency-of-clip (FOC) calculation can be derived using a formula. For a real-life example, an operator walk-mowing at 6 km/h (3.8 mph) with a 15-blade reel turning at 2200 revolutions per minute (rpm) would be cutting with an FOC of 3.098 mm (0.122 in.).
It is important to note increasing (or tightening) the FOC actually equates to a lower FOC value, and decreasing it results in a higher one. This means when a superintendent says he is increasing/tightening his clip rate, he is actually adjusting the FOC on the mower to a lower setting.
Read the full article: A Closer Look at Frequency-of-Clip