If rectangle is chosen, X SIZE will light up on the display. Use the ↑↓ arrow keys to
select the x-size of the duct, then press ↵ to accept the choice and advance to the next
dimension. Y SIZE will light up on the display. Use the ↑↓ arrow keys to select the ydimension
of the duct, then press ↵ to accept the choice and return to measurement mode.
The rectangle will remain lit on the display.