Istvar,

I have contacted the person I knew (he is a long established glider repairer here in the UK).

From his PIK20D Flight/repair manual, repair section page 3 section 9 "Balancing of control surfaces":

This measurement from the hinge line:

Aeleron: 29mm

Flap: 35mm

Rudder: 20 mm

The idea is to balance the surface on that measurement (no tolerances given, but he says Schleicher work on about 10-15%)

For the Elevator the moment should be less than 40g/mm from the hinge line.

Hope this helps.

Rgds,

Derrick Steed