Add score oddities

docs/docs/user/score-oddities.md

@@ -0,0 +1,48 @@
+# Score Oddities
+
+Writing a score tracker is easy. Dealing with 20 years of questionable score storage habits is not.
+
+Here's a collection of weird things that have reared their head. If you've been
+linked here, it's to warn you about this.
+
+## LR2 Auto Scratch Easy Clear
+
+Before ASSIST CLEAR was a dedicated clear type in IIDX, AutoScr would degrade
+the score back down to an EASY CLEAR. This is fine normally, as the score would
+also have a BP of -1 or NULL. You could easily tell when a score was AutoScr
+and correct it.
+
+However. If you then get **ANY SCORE** on the chart without Auto Scratch, your
+BP will be set to a normal value, rather than -1 or NULL. This means that...
+
+```
+EASY CLEAR, BP -1
+then...
+FAILED, BP: 140
+becomes
+EASY CLEAR, BP: 140
+```
+
+And there's no longer any way to determine the score was auto scratched!
+
+## Beatoraja + LR2 DP Random
+
+Beatoraja and LR2 only store the left hand random. They completely ignore
+the right hand one and never store or send it anywhere.
+
+## ARC PB Only
+
+ARC only exports the users best scores for an individual chart. This means
+you can't access individual scores properly, and Tachi has to just assume that
+they were valid individual scores. This means that...
+
+```
+If you get
+EASY CLEAR, 88%
+and then
+HARD CLEAR, 30%
+
+ARC will send
+HARD CLEAR, 88%
+and Tachi will have to assume that is a single score.
+```

docs/mkdocs.yml

@@ -34,6 +34,7 @@ nav:
     - "user/pbs-scores.md"
     - "user/filter-directives.md"
     - "user/lamps.md"
+    - "user/score-oddities.md"
 
     - Statistics:
       - "user/stats/tachi.md"