We start with this innocent looking bit:
Use “1” if you never want to see decimals.
they said. It will be fun they said.
So I did:
I pressed the button, Beeminder told me in its usual bright green status indicator that the Goal was updated. Which…
… it was not, because we are back to 1.0:
Shouldn’t that be “Use 0 if you don’t want to see decimals”? 
And what if you put 1.5 at the display precision field? What’s between 1 and 2 decimals? 
don’t get me started on that field. It’s a horrible user experience also because Safari really wants me to use one of the values I entered in the past. If I click in that field that shows 1.0 and then press backspace twice so I have 1, then a context menu pops up with the history of previously entered values and auto selects its first entry which is 1.0 and if I don’t spot that quickly enough and hit enter, it will use the 1.0.
And yeah, I don’t understand why it’s not just “number of decimal places” or “number of significant decimals” (though I’d prefer the latter) or just a printf format string: "3.02f" for instance would show values like 420.04.
Ah, yes, this is slightly buggy that it changes “1” to “1.0”! Thanks for reporting it!
And to clarify, it’s not the number of decimal places, it’s the amount to round to. So “1” for integery, “0.1” for one decimal place, etc. Theoretically that allows for “10” for rounding to the nearest 10 (negative one decimal places?) or “0.25” to round to the nearest quarter. And “0” should mean “show me full machine precision”. Not that the UI allows those, I don’t think. Gory details on the blog!
I would argue that 90% of people will understand that it’s the number of decimal places, because the help text says “determines how many decimals to display” 
Bee just fixed every complaint in this thread in one fell swoop! 
http://beeminder.com/changelog#3570
