Thanks Bill, I knew that it must be something more or less obvious. Btw.
its not documented in the glossary and the html document, that there is
an overlay setting for this. I was able to make an analemma movie with
the animation function, this function has the "locked on horizon"
feature but no trail feature. It would be really nice to have this
feature with the main star chart. This would also be helpful if the user
changes the time. I always have to set back the Az/El with the goto
function to get the same horizon view.

Markus

Btw. A function to set the window size to 640x480 or 720x576 would be
helpful in making avi's, without some manual fiddling until its right.