20 INPUT "HAVE YOU ALREADY ENTERED A NEW EQUATION OF THE FORM Z=F(X,Y) IN LINE 1000";A$: IF LEFT$ (A$,1)="N" THEN PRINT:PRINT :PRINT " THEN ENTER EQUATION FOR Z IN LINE NUMBER 1000 BENEATH 'Break in 23','OK' MESSAGE BELOW."ELSE 25
21 PRINT " EXAMPLE:":PRINT
22 PRINT "1000 Z=EXP(-(X*X+Y*Y))":PRINT :PRINT
23 PRINT " THEN START PROGRAM AGAIN BY TYPING 'RUN' OR HITTING F2 FUNCTION KEY.":PRINT :PRINT :STOP
25 CLS:PRINT : INPUT "ENTER GRID WIDTH (1-FINE,50-COARSE): 10 ";A$: IF A$ = "" THEN GW =10: GOTO 35
30 GW = VAL (A$)
35 INPUT "ACCURACY (1-FINE,10-POOR): 5 ";A$: IF A$ = "" THEN AC =5: GOTO 50