90: Hold a board against one wall and hold a square or another board with a 90 degree corner against the other wall and scribe a line on the first board using the edge of the 90 degree board. Enter the angle between the wall and the edge of the second board and press the 90 button.

45 triangle: Hold a board against one wall and hold another board with a 45 degree corner against the other wall and scribe a line on the first board using the edge of the 90 degree board. Enter the angle between the wall and the edge of the second board and press the 45 button.

60 triangle: Hold a board against one wall and hold another board with a 60 degree corner against the other wall and scribe a line on the first board using the edge of the 90 degree board. Enter the angle between the wall and the edge of the second board and press the 60 triangle button.

included: The included angle includes all of the object between the two sides.

inside: The inside angle is pi minus the included angle. It is the angle between the walls.

interpolate: The angle that the wall bends, positive for inside. For outside corners lay a board against each wall and scribe a line on one board. Measure the angle from the wall to the other board edge and enter the negative of that number and then press interpolate.

compliment: Enter the compliment of the angle that the wall bends.

There is an illustration for svg enabled viewers, and for others, defining the angles.