This page uses a bit of Javascript I wrote, along with JQuery and Flot to take a simple plaintext datafile, consisting of space-seperated lines like:
2001-12-31 123.4 12.3
Where the space-seperated fields are date, weight, and body-fat percentage. It loads up this data from a file ("fat.txt" in the same directory as this html page) and creates two graphs, with a timespan selectable by the buttons at the top.
This probably only works with recent Gecko browsers (Firefox, etc.) and Safari, because the Flot plotting library relies on <canvas>.
Download fat.html, fat.js, jquery.yui.js, jquery.flot.yui.js, and place them in the same directory on a web server as a file named "fat.txt" with samples, one per line in the format described above.
The two javascript files are from jQuery and Flot, compressed with YUI Compressor. It also uses parts of the Yahoo! UI Library, but it loads them directly from Yahoo's servers as Yahoo! invites you to do.