The meter is really a voltage meter as it measures the return voltage from the coil which also is the voltage for the tones you hear. Now when swinging over a target you may notice the tones are also changing a bit, so the numbers will be too. What you want to do is just wiggle the coil over the target you want to ID and keep the tone as steady as possible, then look at the meter and the numbers should be fairly solid and may jump a number or too, but if deep it will be more numbers as it will be harder to keep the tones steady.When I calibrate my meter to 180 on a quarter it will bounce around 179-180 as I try not to get 181. Air test it will stay around this when you test a quarter or dime, but in the ground it still will ID as this, but maybe see the number jump more as there is other targets or iron it will see, so this is why you try to wiggle only over the target you are trying to ID and keep the tones as steady as possible before you look at the meter for the actual ID.
Go by the tones and try to get a repeatable tone and keep it a steady tone by going only over that target, then look at the meter.