You're probably thinking of INTERCEPT and its sister function SLOPE. You're
also probably thinking that the chart will do these calculations for you,
but you're going to have to get your worksheet dirty.

In two cells, enter these formulas:

=SLOPE(Yrange,Xrange)
=INTERCEPT(Yrange,Xrange)

where Yrange and Xrange are the cell ranges containing your data. These can
be used in the well-known formula for a straight line, Y = mX + b, where m =
SLOPE and b = INTERCEPT. To find the X value at which your line crosses the
constant, invert the formula to X = (Y - b)/m, plug in the constant for Y
and the calculated linear parameters for m and b.

To convert a number to a date, simply apply a date format to the cell. The
whole number is how many days have elapsed since 1-Jan-1900, and the
fraction is how much of the day has elapsed since midnight.

- Jon
-------
Jon Peltier, Microsoft Excel MVP
Tutorials and Custom Solutions
Peltier Technical Services, Inc. - http://PeltierTech.com
_______


"GoodTrouble" wrote in message
...
Hello all,

I have been banging my head against the wall forever on this one...

I have a scatter plot X,Y graph in my spreadsheet. The X axis is dates,
and
the Y, dollar figures (Value over time). The plotting is fine, however I
have
a constant line (cost) which at some point the values will cross. I need
to
get Excel to draw a vertical line, or at the very least tell me the figure
at
which this happens.

I know of the "INTERSECT" and "LINEST" functions, however they are just
returning unusable decimals, I'm guessing due to having dates on one axis.

I am using Excel 2007 Please Help!
Thank You!