What must be done with the power supply before measuring resistance?

Before measuring resistance in a circuit, it is essential to turn off the power supply. This is crucial for several reasons. When measuring resistance, the multimeter sends a small voltage through the component or circuit to determine its resistance value. If the power supply remains on, it introduces external voltage and current into the circuit, which can lead to inaccurate measurements or potentially damage the multimeter. Additionally, measuring resistance with power applied could create hazardous conditions for the technician, as it increases the risk of electrical shock. Therefore, ensuring that the power supply is turned off before conducting resistance measurements is a vital safety practice and helps obtain accurate resistance readings.