Recently I have had problems with the W frequency in my machine (more or less the head balance and probe weight). when adjusting this frequency I kept running into problems with it's variation on initialization of the system. I found several things to keep an eye on while making adjustments.
1) Insure that nothing is touching the machine.
2) Keep the Z axis clamped during adjustment.
3) Do not use the adjustment inside the BitMax for unclamped variation, use the adjustment on the arm.
4) Check the frequency every so often to insure it stays low during clamping. Doing this and adjusting will decrease the time it takes.