Flow show

A flow show is a device on a drilling rig that is attached to the flow line and has a paddle that swings out as the flow of drilling fluid passes by it. The angle of the paddle increases as the volume of drilling fluid increases and pushes it out further and vice versa.
The purpose of the flow show is to allow the driller (and other rig personnel) to monitor the flow of drilling fluid as it comes out of the hole. The reason for monitoring the flow:
See Drilling rig (petroleum) for a diagram of a drilling rig.