UPBs are listed as 1,000 credits for 1,000 UPB, and possess 1 bulk. Do you have to buy them in increments of 1,000? Or could I by 20 for 20, or 100 for 100, or 500 for 500?
It'd be a shame to only need 30 UPBs to repair my 10th-level rifle, but end up having to spend 1,000 credits on 970 UPBs that I didn't need.
Or is it just formatted that way to make bulk tracking easier to work with, and you can buy any number you wish?
The section on UPBs talks about using them as currency. I'd expect you to be able to "convert" any number of credits to UPB, or otherwise purchase in quantities less than 1,000. For ease, I'll probably sell in units of 100.
If it didn't need to be sold in bulk, it probably could have been listed as 1 UPB = 1 credit.
I'm thinking it's expected to bought in bulk, much like 40 credits for 30 small arm bullets. But any GM can say otherwise.
For Starfinder Society it has to be in lots of 1,000 units for 1,000 credits, though.