100 REM DEMONSTRATION 'FILTER'
110 :
120 (null):(null) 15
130 (null) 1,4
140 (null) 1,0,0,15,11
150 (null) 1,700:(null) 1,ON
160 :
170 FOR I=4000 TO 7500 STEP 10
180 (null) T,I,15,1:NEXT
190 :
200 FOR I=7500 TO 4000 STEP-10
210 (null) T,I,15,1:NEXT
220 :
230 (null) 1,(null)