The problem with calculating when desperado moves are involved is that they can occur even when several of the pieces involved are protected, they can be long or short sequences and different kinds of pieces can be involved: i.e. N for a R, R for a Q.
A couple important point were pointed out by Soltis:
1) When the captures are unequal, the winner is usually the player who makes the most damaging capture.
2) If the same kinds of pieces are being captured, the player who makes the final capture is often the one who wins.
He also observed two points to keep in mind when calculating are:
1) The material balance (or imbalance) after each move
2) What's the material situation at the end, which is the last capture?
Keeping track of the material in a sequence of captures can be confusing and you must keep an eye out for surprise moves that end the sequence in your opponent's favor. You might think this would be difficult to keep track of using only ten fingers, but THIS Youtube video might help.
The following game of trap the Queen involves some tricky calculation of desperado moves that's fun to try and visualize. Good luck!