Trendlines no longer forecast

[hthirtysix]

Version: 2008
Operating System: Mac OS X 10.5 (Leopard)
Processor: Intel

About a month ago I was using Excel 2008 to do trendline forecasting in scatter plots. It was working fine and everything. I ended up not using trendlines when I presented it and just stuck with the normal "connect the dots" function of Excel.

Anyway, I start on a new project a couple days ago and finally get to the graphing part of it and Excel won't extend trendlines at all. The type of data is identical to my previous projects, so I figured why not open up those spreadsheets and try--they won't do it any more either. The type of trendline I select doesn't matter either, even a linear line will not forecast.

I can get a line graph or bar graph to have a forecasting trendline, but not scatter, which is what I need

Here's a screenshot of the problem:
<http://img228.imageshack.us/img228/7736/picture10av6.png>

 

[Mike Middleton]

hthirtysix -

In your example, you have X data between 730 and 2900, and you are extending
forward 8 units to 2908 and backward 5 units to 725. With the X axis scaled
from 0 to 3500, it is difficult to see such short extensions.

If you change the horizontal axis scale to display 2880 to 2920, you should
be able to see the extension forward. Or, use a larger value for "Periods"
when you specify the Forecast.

- Mike Middleton
http://www.DecisionToolworks.com