What should always be done to protect the meter from damage when measuring unknown voltage?

Setting the meter to the highest range is a prudent approach when measuring unknown voltage because it minimizes the risk of damaging the meter or its internal components. When you set the meter to a higher range, you ensure that it can accommodate unexpected voltage levels without being overwhelmed. If the voltage being measured significantly exceeds the meter's lower range, it could cause the meter to fail or malfunction.

By starting with a higher range, the meter can accurately measure large voltages while protecting its circuits from potential overvoltage situations. This practice is particularly critical when the voltage is unknown, as it safeguards against the unexpected presence of high voltages that could otherwise harm the measurement device. Other choices may not provide the same level of protection against damage to the equipment.