The DEF FN (DEFine FuNction) command can be used to add a total of 52 new functions to Sinclair BASIC; 26 numeric functions (A-Z) and 26 string functions (A$-Z$). Owing to the internal structure of Sinclair BASIC, the best place to store these functions is in line 0. This prevents the line being accidentally edited or deleted and also gives the maximum possible speed (on a standard Spectrum with no Interface I attached, line 1 can be converted into line 0 with POKE 23756,0). A ROM bug, mentioned on states: The FN error (from ZX Computing Monthly - Toni Baker) which is replaced with