At present we add a day every four years, except when the year is divisible by 100; but if the year is divisible by 400 we treat it as a leap year. This is a very convenient system for decimal chronology.
In effect we are adding 365 + 1/4 - 1/100 + 1/400, which is 365·2425 days to the year, as opposed to the tropical year of 365·2422 days.
If we adopt a similar pattern for years numbered in dozenal notation, adding a day every fourth year except for years divisible by *100, then we end up with 365·2431 days (*265·2E days). Nothing being perfect in this world (apart from me, with which opinion my wife disagrees), this system would be out by one day in *800 years; so if we then knock off a day every *800 years we would end up with 365·24219 days (*265·2TT6 days).
(Ten and eleven, single symbols in dozenal notation, are represented here by T for ten and E for eleven; this is a temporary solution for a Web page until it becomes possible to embed a special font.)