I'm trying to learn and understand how Coulomb found is formula. This is from Wikipedia:

He used a torsion balance to study the repulsion and attraction forces of charged particles, and determined that the magnitude of the electric force between two point charges is directly proportional to the product of the charges and inversely proportional to the square of the distance between them.

Now the question and I didn't found anything about it. How is charged and mesaure the balls? It was before the was batteries (and before volta...) and even if we create electrostatic on the ball, it can be exact number.

In other words: How to do the torsion balance using only the knowledge and materils we had?

I'm trying to learn and understand how Coulomb derived his formula. This is from Wikipedia:

He used a torsion balance to study the repulsion and attraction forces of charged particles, and determined that the magnitude of the electric force between two point charges is directly proportional to the product of the charges and inversely proportional to the square of the distance between them.

Now the question and I didn't find anything about it. How did he charge and measure the charge on the balls? It was before batteries were invented (and before voltages were known) and even if he created charges on the ball, how did he know its exact number.

In other words: How did he use the torsion balance along with the little information known at that time to come up with his equation?