The plexi is set in place and marked with a razor knife.
The razor knife leaves an easy to see mark, but will disappear when the plexi is in place.
Coat both pieces with glue and let dry. Install carefully, the contact glue does what it says.
View from across the room.
It's easy to see through the plexi. I'm not sure if I like this or if I would like it Frosted on the inside. I'll make up a test piece with the scraps.
Here, the white surface of the workbench gives it a frosted look.