One precautionary measure taken when cleaning a monitor is

One precautionary measure taken when cleaning a monitor is to unplug the power supply cable. This means disconnecting the cable that provides electricity to the monitor so that it is no longer receiving power. This is important because cleaning a monitor while it is turned on or receiving power can cause damage to the screen or other components, and it can also pose a safety hazard if you accidentally touch the wrong part of the monitor while it is still powered. By unplugging the power supply cable, you ensure that the monitor is safe to clean and that you won't cause any damage to the screen or other components.