Marvin's Habits have a grade system to let you keep track of how you're doing now compared to how you were doing last month.
How does it work?
This is based on the American grading system, so A+ is the best, then A, A-, B+, B, B-, C+, C, C-, D+, D, D-, and F is the worst.
An A+ is anything about 92.4%, A is above 84.8%, A- is above 77.2%, etc. The confusing part is how percent is calculated. We're looking over the past 30 days and giving you points (capped on 1 per day for daily habits) out of 30 based on what how much of the target you reached that day divided by how much of the target you should have done on that day. For negative habits, this is then weighted so that you get half the points for being beneath the desired target. This is a formula I arrived at by trying to find a system that made sense for all combinations of daily, weekly, etc.; positive and negative; target = 0, 1, or more. Originally I showed a percentage, but showing a percentage using the above formula probably wouldn't match with user expectations (without diving into the formula), so I went with a grade system since the goal is an approximation of how you're doing.
You can set Expectations for how well you want to do on your Habits in your Goals.
As for what expectation you should give yourself, it really depends on whether your Habits are negative and how challenging they are. You'll have to play with the system to see how it goes. Start with a C and go from there. If you find it too easy, bump up the Expectation and then try to maintain it there.