hi, that's a really good question what i think the answer is the three beams are different in size
Please see link it has a good starting point for your Triple Beam Balance as applied to science http://genchem.rutgers.edu/balance3b.html
The weight of the grams
A beam of laser light can be extremely intense, can be focused on a small area, and is of a very pure color. sharp, thin, monochromatic
Always keep your legs stiff and concentrate straight ahead of you. If you are about to fall off the beam crouch lightly, if you are still falling, jump off so that you won't get hurt by falling