The SEG$ function extracts a substring (segment) from  a  string,  leaving
  the string unchanged.

  Example

  Center$ = SEG$(Alpha$, 15%, 20%)

1  –  Syntax

      str-var = SEG$(str-exp, int-exp1, int-exp2)

  The substring in str-exp begins with the character at position  int-exp1
  and ends with the character at position int-exp2.