The Input terminal IN2 is a frequency counter, it can also measure the dutycycle of the input pulse. The input pulse low level should be zero volts, the high level could be between 3 and 5 volts. Terminal SQ1 is a Square wave generator with dutycycle control.
The connection diagram and the results are shown in the figure below. These measurements can be done on the SEN input also. Trying to measure without an input results in a Timeout.