10 CLS: SCREEN 0
20 FOR I = 0 TO 15: FOR J = 1 TO 31
30 COLOR J, I: PRINT "OK ";
40 NEXT J, I
50 L$ = INKEY$: IF L$ = "" THEN 50
60 CLS: SCREEN 9
70 FOR I = 0 TO 63: FOR J = 1 TO 15
80 COLOR J, I: PRINT "OK ";
90 NEXT J, I
100 L$ = INKEY$: IF L$ = "" THEN 100
110 SCREEN 9: SYSTEM