Start testing the levels by selecting Measurement->Test Levels or click the button on the standard toolbar.
Increase the output and input levels until the input level is in the range 30 to 3 dBFS (in the figure below, it is 13 dBFS). If the input level is overloaded, it is indicated with a red lamp on top of the level meter.
The testing of levels can be stopped with Measurement->Cancel or with the button on the standardtoolbar.
Start a measurement from Measurement->Start, or clicking the F2 button or the button on the standard toolbar.