>>10217721
It makes sense once you understand what each stick does. This looks like 15 speed, or possibly a "super 10" transmission with an extra selector for ultra low gear ratios. The left stick is an internal transmission high/low selector. The middle is a standard 5 position gear selector. The right stick is the extra high/low gear selector. The left high/low selector is only used when the right selector stays in high.
With the right and left stick low you go through the first 5 gears using the middle stick like a normal manual transmission.
For gear 6 you put the right selector in to high, leave it there unless accelerating from a complete stop, keep the left in low and move back to position 1. this combination of high and low selectors turns position 1 in to a 6th gear.
Now ill complicate things and turn it in to laymen terms in a moment. The final 10 gears go through the same shift sequence 1-5 but the left stick is added for "in between" gears. In order to use the "in between" gears, the main selector must be in neutral, then you switch left high/low, then you move the main selector accordingly.
so......
left and right stick low + position 1-5 = gears 1-5
for gear 6+ put right stick in high (leave it there), left low, position 1 and progress from there.
once going
position 1 + left stick low = gear 6
position 1 + left stick high = gear 7
position 2 + left stick low = gear 8
position 2 + left stick high = gear 9
position 3 + left stick low = gear 10
position 3 + left stick high = gear 11
position 4 + left stick low = gear 12
position 4 + left stick high = gear 13
position 5 + left stick low = gear 14
position 5 + left stick high = gear 15
or you can think of the left stick as main selector X 1 (for low) and X 1.5 (for high)
don't screw up the sequence by the way. if you do, you'll lose your place, have to come to a complete stop, and embarrassingly progress from there all over.