This routine called INVERT (load invert) and contains three commands to do various inverse video functions. NEG turns the whole screen to inverse video, and if this was COPYed a reverse image would also appear on the paper (ie. silver characters on a black background with the ZX-printer).

If you only want part of the screen to be inverse video the command to use is INVERT. INVERT expects two preceding numbers which are the start and finish character positions for inverting.

Each position represents a possible character numbered from 1 in the top left hand corner of the screen to 736 in the bottom right hand corner.

So enter 16 64 INVERT to see the section of screen between the 16th character (half way along the top line) to the 64th character (the end of the second line) change to inverse video. Another 16 64 INVERT would change it back again. The last command is SWEEP which inverts the whole screen but this time in a sweeping fashion rather than all at once.