It's just like handwriting: whichever arm (left or right) you prefer is the one you should use... When I first bought a keyer (paddle with incorporated hardware to generate the dit's and dah's) it was wired for 'thumb=dit'. My cw tutor however, told me he preferred 'thumb=dah', with the logic that a forefinger is better suitable to trigger the much shorter dit! Thinking of this, I figured this was probably anatomically correct. So before learning to use the paddle, I reversed the wiring... If I had left it the way it was, I'm sure I would have mastered it too. Maybe now it was easier for me and/or I learned faster, I don't know for sure. The only drawback I see is that I need to turn the paddles upside down if I operate somebody else's station

73
Jaap
PA8DX