NT8 HELP! sessioniterator

I'm about to give an example of what i'm trying to do by using currentbar.tostring().

To draw an arrow up on every up bar you do this:

if (Close[0] > Open[0])

Draw.ArrowUp(this, "arrowup"+CurrentBar.ToString(), true, Time[0], Low[0]-5*TickSize, Brushes.Green);

to draw an arrow up on the LAST up bar you do this:

Draw.ArrowUp(this, "arrowup", true, Time[0], Low[0]-5*TickSize, Brushes.Green);

Now my question is, how do I do the same for a plot (AddPlot)?

I want to show only the last instance in an add plot, without iterating itself on previous sessions.
Not sure if I have to do anything with historical, or not, or where to start.

Thanks in advance.