From Tacx's website:
http://www.tacx.com/en/producten/fie...ereedschap.dot
Ingenious tools enabling brake blocks to be set easily to the correct position. For optimum braking power the brake blocks - with the wheel rotating in the forward direction - and the rim are to touch at the correct angle, with a slight toe-in. The BrakeShoe Tuner is suitable for racing and maintain bike wheels, with up to 36 spokes and rims up to 40 mm