it's easy, once you figure which gears to count, you just count the teeth on
the respective gears and divide the number of teeth on one gear by that on
the other. determining which ones to count, in the transmission is beyond my
expertise. i know though that it is as simple as that, once you know which
gears to count.
say you were trying to determine the ratio of a rear axle. that is easy as
there are only two gears. one big one and one small one. the big one will
have 3 to 4 times as many teeth, the exact number being the ratio.
i assume the same applies to the tranny.
good luck. i hope that helps.