Ratchet seems to be off-by-one

[zzq]

@cynrd

I saw something similar. I used ratchet for a do less goal. When I put 0.7 it left 0.6 units only. If the beeminder team needs more details, let me know!

This sounds like it could be a floating-point issue. (Compare How does a goal with a rate of 1 have +2 due?)