I interpreted the question very differently than Jon.

You can "roll your own" trendline with the help of Solver.

Suppose your data set is in A2:B101, with x values in col. A.

Then, designate C1 and D1 as cells that will hold the slope and intercept
respectively.

In C2 enter the formula =$C$1*A2+$D$1. Note the use of both absolute and
relative addressing.

In D2 enter =ABS(B2-C2).

Copy C2:D2 as far down as you have data (row 101 in this example).

In E2 enter the formula =SUM(D2:D101) where 101 is the last row of the data
set.

Now, use Solver (Data | Solver...) to minimize E2 by changing C2:D2.

--
Regards,

Tushar Mehta
www.tushar-mehta.com
Excel, PowerPoint, and VBA add-ins, tutorials
Custom MS Office productivity solutions

In article ,
says...
Hi,

I'm working on a Mechanical Engineering lab with a plot of data in the form
of an absolute value function. Is there any solution to allow Excel to plot
a line of best fit as an absolute value function?