Just so long as you name the decadays so that the first one is zero indexed: https://kybernetikos.github.io/UIT/ (day is in the top left).
Personally I thought that just using the equivalent of week number (again, starting with the 0th) was fine instead of using months / hectodays, but it seems fair to give nullday, unoday, duoday, triday, quadday, quintday, hexday, heptday, octday and nonday names.
Personally I thought that just using the equivalent of week number (again, starting with the 0th) was fine instead of using months / hectodays, but it seems fair to give nullday, unoday, duoday, triday, quadday, quintday, hexday, heptday, octday and nonday names.