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AAT ICAS 2026 ✧ usage guidelines for traditional calendar and clock scales

document note: this document is part of the Integrated Chronological Applications System (ICAS). Alliance for the Advancement of Technology (AAT) provides ICAS standards documents subject to terms of use described in document AAT ICAS 9010. please refer to other key AAT ICAS standards documents accessible via the AAT ICAS web site at for important information about ICAS.

this document describes normative AAT ICAS usage guidelines for traditional calendar and clock scales. please refer to AAT ICAS 2020 for additional important usage guidelines. please refer to AAT ICAS 2200 for additional information about support for the use of multiple scales.


representation of mode for traditional scale formats

to ensure the appropriate representation of ICAS and traditional scales in ICAS methods and applications, developers and users should consider representing particular scales in terms of particular scale modes. establishing good practices for the representation of scales can help to avoid conflicts when representing a traditional scale within the scope of an ICAS method or application.

for example, an Inter-Dial Clock that features ICAS and IDC designations on a user-interface can still feature a traditional scale of date and time, however must clearly indicate a particular traditional dial in terms of a traditional scale mode (for example, 'modeG' or 'modeSMH'). although traditional scales may be represented in terms of ICAS specifications, the use of a traditional system identifier must be used for any implementation of a traditional scale. IDC system identifiers are reserved for scales that implement coherent or semi-coherent decimal expressions of the IDC main unit. an interface must not represent a non-decimal traditional scale as an ICAS scale.

top document updated:

system identifiersdatetime
Uniform CalendarUCUCN 12019 S19 Yellow
Inter-Dial ClockIDCzone(UT)t339 tt050
'ICAS in use' can accommodate calendar and clock formatting 'for all people, for all time'.
day of yearD-o-YAD common year day139
Gregorian calendarGG2019 May 19 Sunday
seconds, minutes, hoursSMHUT08:08:14
style legend


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