Is there a way to have MetaStock place a horizontal line on a chart using code?

 How about:

a1:=20;
a2:=LastValue(a1);
a2

Thanks, that is what I was looking for!

Hi yechiyah

20; will also work. LastValue() is generally not needed for constants, though it certainly wouldn't do any harm.  

When an indicator is also used by an exploration, expert or other indicator and it's required to plot a constant as well as its primary output, make sure that the constant is NOT the last output from the indicator. An Fml() call will only call the LST output, and you probably won't want that to be a constant.

Roy