AC voltmeter scales are usually calibrated to read:

Standard AC voltmeters are deliberately calibrated to display the Root Mean Square (RMS) voltage. This is because RMS is the most practical measurement for everyday electronics, representing the equivalent DC voltage that would perform the same amount of work. Even though the meter's internal circuitry might actually respond to the peak or average voltage of the waveform depending on its internal design, the printed scale on the dial (or the digital programming) is calibrated to output the RMS value for a pure sine wave. If the meter displayed peak or average voltages, technicians would constantly have to calculate the conversions manually to figure out actual power capabilities.