Allow goals that are "per instance" rather than "per week"
I suck at getting places on time. I'd love a commitment device that allows me to have a goal such as:
"Arrive no more than 10 minutes late, 80% or more of the time."
This is the sort of goal that doesn't work on an "N per week" basis, because the number of things I can arrive late to will fluctuate on a daily basis. However it does work on a per-event or per-instance basis; each time a scheduled event occurs, I can simply report a boolean value as to whether I satisfied my goal condition for that event. If there are multiple events per day, I just report multiple times.
Admindreeves (Cofounder, Beeminder) commented
Repeating from Akratics Anonymous:
Have you ever wanted to beemind a ratio, like being on time to more
than half your meetings? Someone asked how to do that recently and I
didn't have a good answer but our own Alice Monday had a clever
Make a Do Less goal for tardiness that has a rate of zero  and then
every time you're late you enter a 1, but every time you're on time
you enter a -1. (If you want to enforce less than 50% tardiness then
being on time might only be a -.5, ie, you need to be on time twice to
balance being late once.)
Slightly convoluted but I think it would work. Has anyone tried such a
thing or have better ideas?
 Or 0.00001 since it won't let you create it with a rate of exactly
0, though you can change it to exactly 0 with the road dial after it's
PS: You could have the slope be, say, 1 per week which would mean you
have to keep your lateness ratio below your threshold *but* you also
get one freebie lateness per week. If you have lots of appointments
that wouldn't affect the ratio much.
Sean Fellows commented
Maybe this is off topic, but how do you handle the data entry for that? I am imagining some kind of crazy combo of calendar integrated with your GPS, but do you just enter it manually? :)
This would be helpful to me as well, though I may have come up with a solution. I just set up a "punctually challenged" goal under the "set a limit" goal type since I also suck at being on time. I just started it so we'll see how it goes, but I picked an arbitrary amount of 30 minutes total that I'm allowed to be late by for the week. If there are more events in one week than another, I'll just have to work harder on being on time more to spread out my allotted 30 minutes of lateness. Day 1 and I'm already 6 minutes into my 30 with one more activity to be on time to this evening, so the next 6 days are going to have to go better than today!