In addition to other great information here about THACO, it’s worth highlighting that it was upside-down.
Lower rolls were better.
This led to magic items giving both pluses and (good) minuses in order to remain consistent in world. Also some curses and ailments gave (bad) pluses to certain rolls.
I would think more people would know what THAC0 is over GURPS.
I miss GURPS.
In addition to other great information here about THACO, it’s worth highlighting that it was upside-down.
Lower rolls were better.
This led to magic items giving both pluses and (good) minuses in order to remain consistent in world. Also some curses and ailments gave (bad) pluses to certain rolls.
It was wildly unintuitive.