pops up the small magnifying glass, as long as the button is
down.
middle button
pops up the medium magnifying glass, as long as the
button is down.
right button
pops up the big magnifying glass, as long as the button is
down.
Shift + left button
change the arrow cursor for a crossbar cursor and
enter 'setting home position' mode. Home position is set when the
button is released. Usefule with the 'Keep Home' feature.