The potentiometer is used as a voltage divider in an electronic circuit. When you turn the dial, it changes the voltage. This potentiometer is made from semi-conductive ink. Current flows through the ink from the 3.3V to pin A7, where the change in voltage is measured. The more paint there is, the more resistance and the greater the voltage drop. The voltage going to A7 is converted into a digital value and stored as a 10 bit number from 0 to 1023. In your sensor, where is the CPX measuring change? Not all the current can get to A7 because of the resistance – where is the rest of the current going?