Hello Muleta, what a good question - I had a variety of chairs being used so there were variables.
The traditional answer is 1 high and 1 low for foot work and 1 - 2 middle springs for arm work - but this is not set in stone as people and chairs and springs have a vast variation of potentials. Normally I use stronger springs for legs and lighter for arms - but I also makes sure the spring tension does not distort the person's form, so here is where the tension is an art form to ba adjusted to fit the client. I know this is not a fixed answer hope it helps anyway.