http://willswing.com/pdf/manuals/om_T2_5th_edition_September_2012_with_assembly_diagrams.pdf

Angle Measurement On the T2C’s: you can also measure the sprog
settings by measuring the angle of the sprog tube, relative to that of the rear
keel. To make this measurement, fully set up glider on a reasonably level
surface and set the VG to full tight. Place a stand under the rear keel so as to
set the rear keel tube, just behind the rear wire junction, at exactly zero degrees
to the horizon. Using a gravity actuated protractor measure the angle of
each sprog tube. Be sure to place the protractor on a part of the sprog away
from the center sprog bracket and neoprene cover, and away from any seams in the
sail, so as not to introduce an inaccuracy in the measurement. (Just forward of
the sprog center bracket on the outer sprog, and just aft of the sprog center
bracket on the inner sprog works well.) The minimum angles should be:

The sprog measurements above represent the stock settings at which the gliders
are set during assembly at the factory.

We have also vehicle pitch tested and flight tested the T2C 144 and T2C 154
at the lower sprog settings below, and filmed the sprogs inside the sail
during flight testing. We have confirmed that at these lower settings the
gliders meet the minimum HGMA Airworthiness vehicle pitch test requirements and
flight test requirements, and we have confirmed that at these settings the
sprog cables are slack in flight at all VG settings, at all speeds from stall to
V_d (max pilot full forward sustainable speed). The sprogs are therefore
not inducing any additional twist in the wing at these settings, and are not
therefore reducing performance in any way, and there is no benefit to be gained
from lowering the sprogs below these minimum settings.

These settings should therefore be considered the minimum settings at which
the sprogs should be adjusted – they should under no circumstances be adjusted
lower than this. See also the section below on “Test flight” and note that the
sprog measurement by itself is not sufficient to determine compliance with the
airworthiness requirements – it is further required that the glider exhibit
positive pitch bar pressure in flight at all speeds between trim and V_d (max
pilot full forward sustainable speed) at all VG settings, and that variations in
other aspects of the glider configuration may require that a higher sprog
setting be used to obtain the required pitch pressures.