10 pixels represents a "meter."
The box on the left should fall at the same speed regardless of frame rate.
The box on the right assumes that it always runs at 60fps (the difference is more significant when you switch tabs).
Until now, my previous projects with gravity (eg Platformre, Penland, Platformludo, and Skribilmondo) have used the system on the right.
My future projects will likely use the method used on the left since it also accounts for potentially slower/laggier computers that don't run the canvas at 60fps (this is extremely apparent in Skribilmondo where a ton of blocks are being rerendered per frame).