The PEN SELECT buttons have multiple functions. If used alone, pressing one of the buttons causes the plotter to store its current pen (if it has one) and to select the pen number whose button was pressed. If there is a pen in the pen holder, but there are no empty positions in the carousel for storing the pen, the pen select request is ignored.
Pressing ENTER before pressing a PEN SELECT button causes the plotter to store its current pen in the selected pen position in the carousel. If that position is not empty, the pen is stored in the first empty position. If no positions are empty, the pen store request is ignored.
The PEN SELECT buttons are also used for setting pen force and pen speed values.