The goal when mounting a binding is to place the center of the foot directly over the ski's sweetspot. This spot is determined by the ski's manufacturer and its testers. Theoretically, this balances you on the ski in the optimal way. If the bindings are too far forward of this point, your tails skid out; too far back and they resist turning at all. If they are mounted unevenly, your tips want to cross.
Women's skiing advocate Jeannie Thoren suggests that the average woman mount her bindings several millimeters forward for easier turning. Some very strong skiers like to be mounted slightly back for better holding power.
Most skis have a mid-sole mark on the topskin or the sidewall. Boots likewise have a mid-sole mark. The boot mark is lined up with the ski mark, a special jig supplied by the manufacturer is locked in place, and screw holes are drilled. This "mid-sole" technique is relatively foolproof.
Some manufacturers, such as K2, Olin and Volant, stick to an older method, known as "toe mounting." Chord length is the straight-line measurement from the ski's tip to its tail (not around the curve of the ski). Divide that distance in half (mid-chord), and that's where the tip of the boot sole goes-regardless of boot size. These measurements should be double and triple checked before drilling! It's critical that screw holes be exactly the right diameter and depth and that proper screws be used. If the drill bit is even fractionally too large, the screws can pull loose. If the ski has a metal layer or mounting plate, the holes must be "tapped" with a special tool so the screws hold tight.
As bindings get more sophisticated and plates or lifters are added, mounting gets more complicated and errors compound themselves. There are more types of screws: some for mounting plate to ski, others for mounting binding to plate. Still others extend all the way through the plate into the ski.
It's worth having a talk with your shop technician to gauge his/her understanding of all the variables.
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