In the attack scope the "10" mark is exactly where the "100" mark is in the obnservation one. However, in the attack scope each smaller division is 2, and not 1. The scale of visible marks goes therefore 2,4,6,8,10 (Marked)
Rangefinding formula for attack scope is:
Mast heigth x
100
________________ = Distance
Scale
Whereas for the observation scope it is:
Mast heigth x
1000
________________ = Distance
Scale
Hope that clarifies it a bit