What is the easiest way to check vane clearance on a drop away rest?

check your vanes out for stripes, discoloration, wavyness. put a little lipstick on your launcher and see if any ends up on the vanes, or foot powder. have your buddy hold his finger at the launcher height as you release an arrow and see if he still has a finger. wait, don't try the last one.

Clearance from what? The cables or the shelf?

put lip stick on your vanes shoot a couple of arrows and look on your rest. if theres any contact you'll see where.

Or baby powder.

Or jock itch powder