The invert command toggles the area of the screen pointed to by int-expl,int-exp2. If the dot (LORES or HIRES) was on, it will be turned off. If the point was off, it will be turned on. The H option inverts the Y axis, so that numbering will commence from the top left hand corner and run down the screen, rather than working up from the bottom left hand corner.
Program Example.
00100 CLS
00110 LORES
00120 INVERT 20,20 : REM Turn the location on
00130 FOR I =1 TO 1000 : NEXT I : REM Simple Delay
00140 INVERT 20,20 : REM Turn the location off
00150 FOR I =1 TO 1000 : NEXT I
00160 INVERTH 40,40 : REM 40 across and 40 down
00170 FOR I =1 TO 1000 : NEXT I
00180 INVERT 40,40 : REM 40 across and 40 up
00190 END