Excel Excel 2003 Trend Equation Error

[samtheman]

Hi guys.

I'm using Microsoft Excel 2003 on Windows XP.

When I fit a trendline on my data, it lines up perfectly with the data, but the equation is TOTALLY WRONG! Here's a glaring example:

I have the following points:
X Y
Row 1 13.44 2.94
Row 2 14.96 5.88

The X values are in column A and Y values are in column B.

So I graph the values, and on the graph the X value correctly matches up with its corresponding Y value. Now, when I tell the graph to display the equation (this is linear by the way), it shows y = 2.94x + 7E-15

y = 2.94x + 7E-15 IS NOT CORRECT! Plug in either X value, and you get an answer for y being in like the 40s, way over 2.94 and 5.88

Is there something basic I might be doing wrong? I cannot believe that Microsoft could make such an obvious mistake.

 

[samtheman]

I found the problem. Here's the rule:

IF YOU WANT TO FIND A "BEST FIT LINE" EQUATION, USE "XY SCATTER PLOT", NOT THE LINE GRAPH.

For some odd reason, the XY scatter plot gives me the correct equation while the line graph gives me a wacky equation.

For those of you who are going to use this to find an equation, keep in mind that excel defaults large scientific numbers (both large and small) to 1 significant figure. This is awful. You will have to format the equation to contain more decimals. You can do this by changing the format to "Number" instead of "General" and ramping up the number of decimals.