(Remember that the middle resistance - 102 or 1002 Ω - will vary with temperature, but the 2Ω wires will not) When the amp measures this sensor, it will measure the resistance between one set of red and blue wires. It will then measure the resistances between the red wires and blue wires. Then divide those resistances by half - since there's two wires and we just want the resistance of one wire. The final result is 102 - 1 - 1 = 100Ω