I'm not entirely sure this counts as a bug, but when using the chart, both sets of data are presented to me as smooth, connected lines. It presents a lot better (and closer to John Walker's original spreadsheet) if the raw data is shown as points and the trendline as a smoothed line. This seems to be less discouraging since it's clear which line represents the true weight and which is just "noise". I was able to accomplish this by changing the chart type to "points only", which altered both sets of data to points. Then, selecting the properties of the smoothed weight set only, I changed the line style from "none" to "continuous" and the point icon from "diamond" to "none". This made the chart look a lot more like a scatter plot with a single trendline, rather than two trendlines. I should mention that I use Lotus Symphony as my office software. But since it didn't give me any incompatibility warnings, I have to assume that the .ods standard was maintained and that OpenOffice.org should have similar options.
I am using Windows 7 (Home Premium Edition), IBM Lotus Symphony Spreadsheet v3.0.0, English (US), WTODS v2.2.2, Macros enabled, fresh sheet.
