Disk Utility benchmark, x-axis undefined

From the context, I'd say it's the time axis. However, measuring time in percentage almost seems intentionally confusing.

http://xkcd.com/833/

My guess is that for the hard-to-see zig-zag line, the x-axis represents disk addresses from 0% (beginning of the disk) to 100% (last block on the disk), not time. The y-axis for that line is on the right, in milliseconds. It seems to be a continuous trace of (%-of-disk, seek time) points, all linked together in a chain, chronologically.

This contrasts with the left-hand y-axis which is in MB/s and applies to the blue line across the top. I agree that the x-axis percentages in that case refer to time: the percent of the test period for each point. Rather odd, I agree.

The data points for the most recent benchmark of each disk are cached in ~/.cache/gnome-disk-utility/drive-benchmark/*

The text should explain this, and in addition, the axes should use the same color as the lines.

My other suggestion is to change the colors used for the zig-zag line. I'm red-green colorblind and find it nearly impossible to see them.

Note: I also wish those benchmarks were archived, not just cached. See a related request for that at
 "How can I log my SSD's read performance over time? - Ask Ubuntu - Stack Exchange"
   http://askubuntu.com/questions/8279/how-can-i-log-my-ssds-read-performance-over-time

Note also that the name of the gnome-disk-utility executable is "palimpsest".

+1 to archiving!

If the X-axis is %time for the benchmark read/write then why does it typically decrease over time?
Surely the X-axis is the read/write speed at different positions 0-100% across the disk, like access time?