Your comment indicates that you don't understand the basics of how precision scales are made. For example, in a precision scale the distance from the center bearing to the bearings that support each of the pans must be equal to within thousandths of an inch. And once the scale is constructed, you have to perform an "equalization" procedure to calibrate it.
In "The Homemade Sleeter Centigram Balance" I show you how, with simple hand tools, to make EXTREMELY fine and accurate bearings. Then, with a simple hand-made jig, I show you how to properly adjust the distance between the center bearing and the pan bearings. And finally I walk you through the equalization procedure, and I even show you how to make your own comparison weights.
The Dan Williams scale in the link you provide is alright for the crudest weight comparisons, but it's not a PRECISION scale.
In contrast, the Homemade Sleeter Centigram Balance is accurate to 1/100 of a gram, and that means that it's TEN TIMES AS ACCURATE as an Ohaus triple beam balance. To better-illustrate what I'm talking, here are some excerpts from the section describing the equalization procedure. ------------------------ "An equal arm balance is a precise piece of equipment, and before you can use it you have to adjust it properly. Assuming that the bearings have been properly spaced, the main requirements are that the beam and the pointer swing freely, and that everything to the left and right of the primary bearing pull down on the beam with equal force. When these requirements are met, the balance functions properly. When the cups or the bowls are empty, the beam rests level, and the pointer comes to rest on the center mark of the paper scale. When the forces are unequal, the balance tilts to the left or the right. When you first assemble one of these balances, it always tilts to one side or the other because one side is always a little heavier than the other, and you have to compensate by adjusting the pointer and adding weight to the bowl opposite the tilt. I call the procedure for doing this "equalization", and I separate it into five steps that I call: pointer adjustment, preliminary zero, equal mass creation, equal mass adjustment, and final zero.
...Now turn off the room air conditioner, and close all the doors and windows. The balance is very sensitive, and small air currents will make equalization impossible...
Hint. As you apply the vinyl tape, you'll experience the sensitivity of this balance for the first time. The slightest touch will set the beam in motion, and you may find it difficult to make it come to rest. Experience has taught me that raising a finger slowly and gently under each bowl is the most effective way to stop the beam's motion."
David Sleeter/Teleflite Corp.