Suppose we setup a potentiometer with two power supplies +10V and -10V as shown above. A digital voltmeter is setup to measure the voltage.
If the potentiometer is turned all the way up, a digital voltmeter would read +10V, if the potentiometer is setup all the way down, the digital voltmeter would read -10V.
My question is
When writing the equation for calculating the voltage across the voltmeter, how can we include the +10V and as well as -10V in our potential divider equation and calculate the voltage at the voltmeter?