Common Calendar


Civil timekeeping demands timestamps with sufficient information to represent accurate local time.  We present a system called Common Calendar Timestamp System (CCT) that produces binary and character timestamp formats providing technically accurate and human readable local time incorporating Coordinated Universal Time (UTC) leap-seconds, time zones and geographic coordinates.

CCT is organized into layered specifications to provide clear guidance on the interpretation of International Earth Rotation Reference Systems Service (IERS) leap-seconds, Internet Assigned Numbers Authority (IANA) Time Zone Database (Tz Database) information and GIS coordinates, algorithms for UTC calculation, binary and character timestamp formats, methods for populating and reading the two formats, and a high-level Application Programming Interface (API) for convenient manipulation of calendaring operations. 

The binary format is a compound counter composed of [day-number][leap-seconds][time-of-day] with additional local time metadata to enable efficient machine interchange. The character format is a human readable form with additional metadata reflecting the information in the binary format. For example:


CCT is designed to satisfy people's expectations by representing the local time as known to the emitting system. The formats are designed to facilitate calculation of time marks within the current day without need for access to external metadata. Normalization to UTC is an inherent quality.  Geographic coordinate data may be included to provide traceability provenance for 4D GIS applications.

Central to the CCT implementation is incorporation of the open source Tz Database data and code.  The local time rules in the many time zones all over the world are quite complex.  Tz Database has undergone years of development to accommodate these intricate variations and is used directly or indirectly in most operating systems and timekeeping implementations. CCT now employs its functionality for interoperation with existing systems such as Linux, Apple and Android. CCT supports use of Unicode Common Locale Data Repository (CLDR) to map Tz Database time zones to Microsoft Windows time zones.

CCT treatment of UTC is implemented with counting methods to accommodate the common practice of leap-second introduction in local time simultaneous with UTC or "rolling leap-seconds" as used by some systems. It also can accommodate the variations used by NTP and Posix time. Negative leap-seconds are supported.

Common Calendar Timestamp provides a robust timestamp system for general purposes and may be implemented with sufficient accuracy to satisfy financial regulations and be suitable for use as legal time and traceability provenance. The author hopes the proposal may find support for standardization and looks forward to the community's suggestions for refinement.


Common Calendar Specification

UTC Based Local Timescales

Brooks Harris Version 9 2024-04-27


Common Calendar Introduction and Scope

Common Calendar Date and Time Terms and Definitions

Common Calendar TAI-UTC API

Common Calendar YMDhms API

Common Calendar Time Zone API

Common Calendar Local Timescales

Common Calendar Binary Format (CBF)

Common Calendar Character Format (CCF)

Common Calendar Timestamp API

Common Calendar Geostamp


CCT c/c++ Reference Implementation

Common Calendar Reference Implementation Guide

CCTDemoConsole Tests Listing Guide