Which of the following precautions should be taken when measuring high voltages with a voltmeter?
Why Voltmeters and their test leads carry voltage and category ratings that reflect how much insulation and creepage distance they have. Exceeding that rating can cause arcing across the probe insulation or inside the meter, which can injure you or destroy the instrument. Before touching a high voltage circuit, confirm both the meter and the leads are rated at or above the voltage you expect to see.
Watch out Low impedance is the opposite of what you want in a voltmeter: a good voltmeter has very high input impedance so it draws almost no current and does not load the circuit being measured. A voltmeter is also never meant to be the ground path for a circuit, and meters are not 'set to a frequency'.
The leads count too. Meter AND leads must be rated for the voltage you are poking at.