Take a compass, set the radius to the longest chord of your rudder, then draw a quarter circle arc. Put a radius line from center of arc to midpoint of circle, to represent your neutral rudder position. Measure along the circumference of the arc the 110 mm, from neutral to either side, and mark the circumference at one of those points. Draw another radius from the mark to circle center. The angle between that line and the neutral line is the angle they are recommending.

Regardless of what the recommendation is, I would set up for thirty degrees to either side, since anything above that is most likely going to stall the rudder anyway. Pattern ship is not a 3D model, does not need extreme rudder throws. Then, as bla bla says, adjust to suit your preference after flying it awhile.

It is ridiculous for mfrs to give recommendations like this without specifying the method of measurement. Those who know will ignore the recommendations no matter what they say, and those who don't know need the instructions to be more explicit. This is another contribution to the RC industry from the legal profession.