lorain's guess makes sense to me.

Either way, 3 oz of oil isn't going to make much difference either way.

I don't really understand the "saving" it aspect; if you're anal (like many of us) you'll pour in 8.5 USQ and have a half-bottle hanging out in the trunk. I do know some who just dump in 8, and then add a quart when it drops, though. Again, that 3 oz won't make much of a difference...even assuming it does come out of the bottle.

Just dump that .1 into your diesel tank, at least you won't feel like you've wasted any oil, and you can use the old empty containers to store your old used oil before disposing of it.