1. Each spirit has a Force, which indicates it's power (As a general descriptor. A Force 4 Spirit is like saving a Level 7 Fighter). The force determines the strength and abilities of the spirit, as well as the difficulty to summon and control.
2. The sorceror rolls his casting power. Each success indicated one "service" the spirit owes the summoner before he departs.
3. The drain is based on the force of the spirit.
This is ripped right out of Shadowrun. The problem is ST uses fixed difficulties, where in Shadowrun, the tartget number when you roll your casting pool is determined by the strength of the spirit. That's something we'll have to figure out.
Straight from SR:
My suggestion is a change on the drain procedure, at least for conjuring. Before we did (Drain Dice - Resolve), and each success was a non-lethal level. NEW IDEA: Drain = the Force (Ftagn level) of the spirit, *reduced* by successes rolled on resolve.
In last night's case. Ftagn 4 Spirit = 4 levels of non-lethal. Soaked by success on a Resolve roll. Perhaps allowing dice from the casting pool to be withheld.