If you measure the way Tony says you are missing something in my opinion.
Different combinations of spreader arm length and angle can result in a same distance from chord to mast.

Therefor I would suggest to measure:
- Spreader arm length (from mast to wire)
- Distance from chord to mast
- tension on diamond wires
- prebend in the mast (result of the above)
(and ofcourse windspeed and crewweight).
For easy comparison Spreader arm width is also handy.

Any one interested in a comparison?
Send it to me and I'll gather the info in an excell file.

(The Capricorn has only a couple of lines on diamond settings but very understandable and interesting ones).

Gill