On the E70, there are two stages on the brake pad sensor, and the indicator jumps when they contact. In between those steps, the computer estimates brake pad life based on brake use.

I wouldn't worry about it until the last stage trips, and you get a light telling you they are worn out, and it is time to have brake pads replaced. It takes too much energy to try and figure out what the computer is calculating in between, IMO.

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2007 X3 3.0si, 6 MT, Premium, White

Retired:
2008 535i, 6 MT, M Sport, Premium, Space Grey
2003 X5 3.0 Steptronic, Premium, Titanium Silver
2002 325xi 5 MT, Steel Grey
2004 Z4 3.0 Premium, Sport, SMG, Maldives Blue