The math symbols on the Bionicle dictionary indicate a base-6 system (heximal?). The numbers 0 through 5 are all based on a circle with a dot in the middle. 6 through (presumably) 12 are the same as the 0 through 5 but with a circle around the (...) (23 years ago, 21-Mar-01, to lugnet.technic.bionicle)
While the digits are base-6-ish they are used as base 10. i.e. "10", made up of a "1" and a "0", comes after "9". It would be kind of cool if it really were base 6, but no doubt Lego doesn't want to confuse the non-math inclined people out there. (...) (23 years ago, 22-Mar-01, to lugnet.technic.bionicle)