okay... So, the quantity of slurry just fit when you poured the whole slurry into your quart-sized mason jar?

If so, I'd say, from the Mr. Malty site above, that, if you add sanitized water back to your mason jar, then you're at "thin" on the calculator.

--or--

Do the math to determine what you need to set the slider on for your yeast...

Do some math... let's make a basic beer in the calc. a 1050 ale. On "thin", you'd need 214ml.

A mason jar is 30oz or 887ml. If you need 214ml, then that's 25% of the mason jar shaken up.

There are 29.6ml per oz. So, on default, you have 8oz or 236.8ml and you need 25% of that quantity, or 59.2ml.

Sliding the slider along until I reach 59.2ml results in a setting of 3.5. Now you'll know where to set the slider when your yeast looks and acts like the yeast you have.

It doesn't seem reasonable to work the math back, so I'd just take the slurry from your beer, set it to thin in the calc and use that for your slurry. Or I'd let it sit for a day and use the default. It's great to try to get as good as you can but a little bit goes a long way.