measuring @ the arena

[EricH]

Unless, of course, it is part of the robot.

Note that such devices attached to the robot would fall under extra scrutiny at inspection to ensure that they can't leave the frame perimeter during a match. It is also quite possible to have a ruling that you could not extend it before the match.

Your best bet would be to do a quick-and-dirty open sight across the top of your robot--block with a slot here, pin there, line them up through the middle of the balls, hope you fire correctly. If that would prevent you from going under the tunnel, use servos to move them out of the way during the match.