Selecting Transiting Planet or Degree
The radio button at the top of the Alerts tab specifies whether you are setting a transiting planet alert or a static degree crossing alert. The controls below change depending upon which is selected:
Because the "Transiting Planet crosses and Angle" button is selected, a combo box with "Transiting Planet" appears. If you select the other button, then two fields appear for Degree and Sign as shown below:
The latter case is for setting up a static degree crossing alert.