How to put last value on plot?

I have a real time plot that updates periodically (ie sin(x)). I want to have the ability to show the last x & y value at the end of the plot. This value will update periodically as the plot updates.

For example,
if my plot is a straight line ------------------------------------
(100, 0)

The (100, 0) is the last value I want to show.
When the next update comes ------------------------------------
(101, 0)

I would see (101, 0)

How can I do that? Thanks.