I like setting my Variability & Limits controls at the max (10) to allow the machine to give the highest/widest tones for all signals in the ground. That will allow you to hear subtle differences, but even at the max settings, you will not be able to tell 100% of the time differences between clad and silver quarters. Even the deep clad dimes and later copper/wheat pennies will give "silvery" sounds that alert you to "dig". And very worn silver dimes (barbers, etc.) will sometimes sound like a penny. You just never know.....you gotta go for the deeper, higher toned signals (greater than halfway down on the sensitivity meter). At the parks I detect, if I spent my time digging shallow penny/dime targets, I would definitely have less old coins at the end of the day. I've dug over a thousand silver coins in the past couple of years, and let me tell you that I was surprised many, many times to see a silver coin in the bottom of my plug. And the opposite holds true too....many times I thought I had a silver coin target, only to find out it was a deep memorial penny or clad dime. So if you dig all those high tones, shallow or deep, you will have higher confidence, but not 100%, later on when telling if you have a silver coin under your coil.
Good Luck!
HH,
CAPTN SE
Dan