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

2 as far down as you have data (row 101 in this example).
In E2 enter the formula =SUM(D2

101) where 101 is the last row of the data
set.
Now, use Solver (Data | Solver...) to minimize E2 by changing C2

2.
--
Regards,
Tushar Mehta
www.tushar-mehta.com
Excel, PowerPoint, and VBA add-ins, tutorials
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In article <4E61A885-7B12-4C0D-A58F-(E-Mail Removed)>,
(E-Mail Removed) 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?
>