PjD1st's grading system differs from the rest of the mainline games in that rather than being graded primarily on accuracy, your grade (between CHEAP, STANDARD, and GREAT) depends entirely on your score (save for PERFECT which requires a full combo and MISSXTAKE which happens when you die).
Here are the score gains per note judgment (assuming you hit the correct button - values for correct timing but wrong button are in parenthesis):
| Judgment | Timing Offset | Score |
|---|---|---|
| COOL | 0 sec | +500 (+250) |
| FINE | ±0.03 sec | +300 (+150) |
| SAFE | ±0.07 sec | +100 (+50) |
| SAD | ±0.10 sec | +50 (+30) |
| WORST | ±0.13 sec or more | 0 (0) |
In addition, you get bonus points based on your combo. Points are added per note based on what range your current combo is in. If you break combo (such as hitting the wrong button or getting a judgment of SAFE or lower), no bonus points are added.
| Combo Count | Score Bonus per Note |
|---|---|
| 0-9 | 0 |
| 10-19 | +50 |
| 20-29 | +100 |
| 30-39 | +150 |
| 40-49 | +200 |
| 50+ | +250 |
Finally, there's CHANCE TIME, which allows you to stack up massive amounts of points to your score just by keeping up your combo. This is the main factor that separates STANDARD and GREAT. If you break combo during CHANCE TIME, you're gonna have a bad time. It works like this:
| Note Count | Score Bonus per Note |
|---|---|
| 1 | +100 |
| 2 | +200 |
| 3 | +300 |
| 4 | +400 |
| 5 | +500 |
| ~ | ~ |
| 50+ | +5000 |
As you can see, for each note added to your combo (starting with the first note in the CHANCE TIME period), that's multiplied by 100 and added to your score up until note 50, after which +5000 points are added per note. That's in addition to the aforementioned bonuses for normal note judgments and combo. A lengthy CHANCE TIME can create a huge disparity between score borders.