I can gather I was shorted 1/2 of a tenth.
Nope.

All we can assume is that your "quarter" weighs more than .2oz, but less than .3oz.

Your scale could be dead on. (don't really know...)
And your "quarter" could weight exactly a quarter oz. (.25oz.)

Think about it: how's your scale gonna display .25 when it can't show enough numbers?

You need a scale with more precision, for weighing such small quantities. It's like you're trying to weigh a sesame seed on a scale that's designed to weigh an entire Big Mac. Or, to put it in terms Hermie can relate to, it's like trying to weigh a stripper on a truck scale. She's too light to even register on the truck scale, but does she weigh "zero?" My face says differently.

Let's continue this analogy, because Hermie is now having pleasant mental pictures.

Let's weigh the dancer on our bathroom scale. It says she weighs 120 lbs, in her stiletto heels with a pocketful of condoms. Let's ask her to "hold" our quarter oz. What's the scale gonna say? 120.015625 pounds? Naw, it's probably still gonna say 120 lbs.

Let's say she decides to dance for us, and we start giving her dollar bills. (Dollar bills weigh about 1 gram each.) By the time we've tipped her about 454 bucks (usually about 10 minutes if Hermie thinks she's hot) she'll trip the scale at 121 lbs. Is this making any sense?

Or, do like NextLine sez and get a scale from the headshop.

Your current scale cannot tell you what you want to know.

BTW, WTF is a "granual?" You made that up, right?