The compression on the screen frequently eats lines. You can try zooming to
see them, but depending on how much it it reducing, you may even see them in
this case.
Turn off your grid to see what is really there without the preview. (I
always add the "toggle grid" button to my toolbar.
Thanks much. Zoom solves most of the problem. Preview still doesn't show
exactly what will print (line thickness, etc.). But Zoom does help. Thanks
again.