The basic scenario for this button is this.
The user selects the object.
Press the button 2.
The program LabPP_GoodwinGDL prompts the user to specify the first point of the line segment, then the second.

Algorithm No. 1

Then calculates the slope angle of the segment.
The angle is measured from the direction down. The values range from -180 to 180 degrees. Clockwise - in plus, counterclockwise - in the negative.
The program then writes this angle in degrees to the object in the GoodwinGDLAngle parameter.