Summarize this article:

Choose one that matches the setting you chose on your voltmeter's knob. If there is no exact match, read from a scale that's an easy multiple of the setting. For example, if your voltmeter is set to DC 10V, look for a DC scale with a max reading of 10. If this isn't available, find one with a max of 50. This is a linear scale just like a ruler. For instance, a needle pointing halfway between 30 and 40 indicates a reading of 35V. Skip this step if you are reading from a scale that exactly matches your voltmeter's setting. Otherwise, correct for the difference by dividing the printed scale's max value by your knob setting. Divide the number the needle points to by your answer to get the actual voltage. For example, if your voltmeter is set to 10V but you are reading off a 50V scale, calculate 50 10 = 5. If the needle is pointing at 35V, your actual result is 35 5 = 7V.

Summary:
Find a voltage scale on the needle's dial. Estimate the needle's position based on nearby numbers. Divide your answer if using a different scale.