This is a great tool, if you can spare the time and materials to assemble it.

Contrary to the instructions, I was able to construct a working one with very minimal tools; I printed on regular copy paper then stuck the paper to a cut-up cereal box with a regular glue stick. I used a paper clip - bent and clipped with wire cutters - as a spindle for the wheel itself, and sealed the device (and fixed the spindle) using electrical tape. I will seal it more firmly with a stapler when I can.

From a raw usability standpoint, it's quite good, but there are some issues:

• Due to the material I used, the numbers are quite deep into the device, and may be hard to read in low light
• The large numbers (%age "yes") are perfectly legible; however, when the background is dark, it can be difficult to read the small numbers. This is especially egregious at the "has to be" and "impossible" probabilities at chaos level 8, which are almost completely illegible. This could be fixed by using black-on-white universally (as at chaos level 1); or by adapting a better color scheme (such as white-on-red) for high chaos levels; or by using white when the background is black.
• The small text looks a little smudged; I blame my inkjet printer, but it would be nice if the instructions were a few pt bigger as they would then not suffer as much from this issue.

The second issue prevents me from giving it a full 5 stars.