This code system (http://hl7.org/fhir/v3/CalendarCycle) is defined as part of HL7 v3.
This value set has an inline code system http://hl7.org/fhir/v3/CalendarCycle, which defines the following codes:
Lvl Code Display Definition
1 _CalendarCycleOneLetter CalendarCycleOneLetter CalendarCycleOneLetter
2 CW week (continuous) week (continuous)
2 CY year year
2 D day of the month day of the month
2 DW day of the week (begins with Monday) day of the week (begins with Monday)
2 H hour of the day hour of the day
2 M month of the year month of the year
2 N minute of the hour minute of the hour
2 S second of the minute second of the minute
1 _CalendarCycleTwoLetter CalendarCycleTwoLetter CalendarCycleTwoLetter
2 CD day (continuous) day (continuous)
2 CH hour (continuous) hour (continuous)
2 CM month (continuous) month (continuous)
2 CN minute (continuous) minute (continuous)
2 CS second (continuous) second (continuous)
2 DY day of the year day of the year
2 WY week of the year week of the year
1 WM week of the month The week with the month's first Thursday in it (analagous to the ISO 8601 definition for week of the year).