Trendline

I think there's a few things to consider before taking this route and using the results for your analysis:

1) Excel does not natively allow chart trendlines to go through the origin because that inherently takes away the point of a trendline - to match the data given. If your trendline is behaving poorly, this is usually a result of poor data (or rather, poor instrumentation). It is important to note that by altering a trendline to go through the origin fundamentally alters the forecasting capabilities of the trendline, whereby you degrade what the capability is actually used for.

2) It is not uncommon when testing empirical data that you void the first few samples of data while the test runs. This is to reduce noise and obtain precise results. By inspection, it appears this is what the case is with your data, so I would recommend starting with row 4 data in your sample workbook instead of row 2.

3) Ultimately, since this is your data and not mine, I can only give recommendations; after all as far as you know, I'm just some schlub on the internet. If you are truly set on creating a trendline through the origin, I know LINEST can be used, albeit through some manipulation. This link describes a similar process I have used: http://www.oooforum.org/forum/viewto...ight=trendline

Hope this helps!