Plot lines not accurate

["Michael J. Doiron" <75534.2410@xxxxxxxxxxxxxx>]

All,

I'm having some trouble with my plot lines not representing the correct
values.  For instance if I plot 3 ROC's, a 10, 20, and 30 period, in the
same subgraph the 20 period ROC will plot below the zero line while the
data window shows the value to be above zero.  Sometimes they move
(relocate) when I scroll across the screen (but not to the right place). 
They aren't stable and makes it impossible to visually check out a chart
and see what's happening.  Any ideas? 

Thanks,

Mike