The point on the stone shows if the sliding delivery was on the line from the beginning to the release.
Sliding off the line, inside-out / outside-in releases and many more problems are very well visible.
This device is for practise alone, the player can see if line and release is fine.
Perfect for precise setting up drills and practise.
Pointing laser built in a broom gives you a free standing target.
Perfect for realistic video practise.