Variable Resistors in a Voltage Divider

[PsychonautQQ]

My textbook says that in a voltage divider (voltage source Vin, then a resistor, then another path that leads to Vout, Resistor two, Ground, that it is a bad idea to use variable resistors for BOTH of the resistors (but it is okay if you just do one or the other). Does anybody know why?

 

[berkeman]

My textbook says that in a voltage divider (voltage source Vin, then a resistor, then another path that leads to Vout, Resistor two, Ground, that it is a bad idea to use variable resistors for BOTH of the resistors (but it is okay if you just do one or the other). Does anybody know why?

What happens if both potentiometers are set to zero?

 

[Integral]

With 2 variable resistors there is a possibility of having 0 ohms resistance, this could damage your power source.