I've got a series of data on a line graph. It's nothing too rancy - dates and
rates.

3/1/2006    4.660
3/3/2006    4.710
3/6/2006    4.760
3/7/2006    4.810
3/8/2006    4.780

The rates are on the X axis and the rates are on the Y axis. What I'd like
to do is plot a horitzontal line across the chart at a given Y value. Say,
4.630. I know I could add a second data series:

3/1/2006    4.630
3/3/2006    4.630
3/6/2006    4.630
3/7/2006    4.630
3/8/2006    4.630

But that seems like an awful lot of extra work for a simple horizontal line.
especially since my actual dataset is quite large. Is there a shortcut way in
Excel I can tell it to just plot a line at a given Y value? Thanks.