The GOSUB verb transfers program control to an internal subroutine and branches unconditionally to the specified program line using the same logic as the GOTO.
Branch line number.
PRO/5 saves the location of the GOSUB on the FOR/GOSUB stack. To exit a subroutine, use a RETURN statement to return to the statement that follows the GOSUB. An EXITTO can also be used with a line number for the program to continue. Both RETURN and EXITTO pop the FOR/GOSUB/WHILE stack one level.
1000 GOSUB 2500
2500 REM SUBROUTINE
2510 LET A=50; LET B=A*C/2; PRINT B