Fully Commented Commodore 64 ROM Disassembly (German)

I thought "let's check my knowledge of 6502 code by looking at a simple function", and chose http://www.pagetable.com/c64rom/c64rom_de.html#BC58. That got me:

  BASIC-Funktion ABS
  .,BC58 46 66    LSR $66         Vorzeichenbit löschen
  .,BC5A 60       RTS             Rücksprung

I don't call that "fully commented". A logical shift right of memory at $66 clears the sign bit? Show me your data structures, please.