Could you refer to the following program? ACLS SPSET 0,0 POSX=200:POSY=120 WHILE TRUE VSYNC 1:STICK OUT SX,SY DX=SX*(ABS(SX)>=0.125) DY=-SY*(ABS(SY)>=0.125) POSX=POSX+4*DX POSY=POSY+4*DY SPOFS 0,POSX,POSY WEND