.83 of what? A dry pack of yeast? As others mentioned, if it's a pack, then use the whole thing. Not all packs are the same size, so it's an odd way to measure yeast. Typically dry yeast is in grams and liquid yeast is actual cell count.
I don't recommend storing dry yeast once it's been opened (manufacturers do not recommend). It will do okay for a week or so, but once the package is open and it's exposed to oxygen, it begins to degrade. So when it doubt, dump the whole thing.
Rite Brew has the lowest prices on yeast. They must move a ton of it, because it's usually very fresh.
https://www.ritebrew.com/