The guy asked for help, so give it to the mm - it isn't that difficult to screw the the spring adjuster and get it accurate.
When the person has learnt a heap about suspension they'll start adjusting further.
Oh, and why is our bike suspension setup different to a mx or road bike ?..... Oh and don't worry about jetting, bar position, tyre air pressure, riding technique, etc....... it's only trials after all. Flipp'n heck.
O.K., I think I get your point (although you lost me on the last sentence), I'm yapping about "theory" and what this guy needs is information concerning "practice".
First, contact your dealer and get the actual suspension travel measurements, front and rear, for your particular make, year and model. Figuring a third of that is easy. It will also depend on the type of fork, so they are not all the same, for instance a TECH fork has about 165mm of travel and a 40mm Marzocchi has about 177mm of travel.
Measuring the fork setting is fairly straight-forward (measure on the tube) but rear setting is a little tricky. The rear wheel does not move straight up and down, it moves in an arc around the axle pivot, so you measure from the center of the rear axle to a point, maybe 4-5" forward of straight up on the fender (the measuring tape is canted forward at the top), which will give a little more accurate measurement.
When you measure sag on a RR or MX bike, it's usually butt-in-the-saddle. A Trials bike does not have a "saddle" per se, and I like to set sag with the rider standing up and placing enough weight on the bars to mimic the approximate stance he/she would use riding (if you don't weight the bars, the front will probably be closer to 1/5th travel). If the sag is close, the bike will lower and raise front/back equally when the rider bounces, also placing weight on the bars in the process.
Does that help a little?