Thinking about how your fingers move vs your thumbs you get way more leverage and movement with your fingers and if you’re trying to push with your thumbs

Yep, I’m thinking about it and I reckon I’ve got more than enough movement in my thumb to make it work given the right design.

This is all rather a moot point given that nobody has ever made one to work out whether it would be any good or not.

I also think you’d struggle to keep your thumb on the lever on wild rough stuff.

Accurate and calibrated scales for all