Well... using this formula
Overall Drive Train Ratio = (# teeth on spur gear / # teeth on pinion gear) x Tranny Gear Ratio
and using a 78 spur and a 26 pinion the manual says it gives a overall gear ration of 9.17:1
So Ive worked it out that the internal gear box ration is 3.05:1.
Plugging this back into the formula gives a Overall ration of 9.15:1 so I think its right.
and who says you'll never use A-Level maths again 
(actually I think that was more GCSE level 
)
Mark