[LEAPSECS] Common Calendar Time (CCT) - timescale design -Brooks Harris

[Brooks Harris]

I've renamed and reorganized the proposed "timescales" of CCT to reflect 
the responses I've gotten and to hopefully make the intentions clear. I 
had used the terms "proleptic UTC" and "proleptic TAI" and these are now 
renamed.

There are other important elements the CCT proposal, including counting 
methods and local time, but this posting is limited to the topic of the 
primary timescales used in CCT.

The main objective of the CCT design is to recast TAI and UTC into a 
more unified specification appropriate for time-keeping from 1972 
onward. It does not represent accurate date-time prior to 1972. In 
addition to maintaining reverse compatibility to TAI and UTC it also 
defines the relationship of other important timescales to TAI and UTC.

The design intentionally sweeps aside the developmental history and 
historical values of TAI/UTC, defining two new scales -

Common Calendar Time (CCT), defined as Coordinated Universal Time (UTC) 
after 1972-01-01T00:00:00Z (UTC).
Proper Atomic Time (PAT), defined as International Atomic Time (TAI) 
after 1972-01-01 00:00:10 (TAI).

These map directly to the current definitions of TAI and UTC after 
1972-01-01T00:00:00Z (UTC) = 1972-01-01 00:00:10 (TAI).

The second important aspect of the design is to explicitly define the 
offsets of important timescales to 1972-01-01T00:00:00Z (UTC) and 
1972-01-01 00:00:10 (TAI), in particular to the origins of NTP, 
1588/PTP, and Unix/POSIX. The design declares two scales that 
immediately precede the origins of CCT and PAT -

Anterior Common Calendar Time (ACCT), defined as a 1Hz scale before 
1972-01-01T00:00:00Z (CCT).
Anterior Proper Atomic Time (APAT), defined as a 1Hz scale before 
1972-01-01 00:00:10 (PAT).

(These terms replace the earlier "proleptic UTC" and "proleptic TAI").

ACCT and APAT are both 1Hz timescales extending into the indefinite 
past. They are artificial constructions for computational convenience 
and have no accurate relationship to date-time before 
1972-01-01T00:00:00Z (CCT) = 1972-01-01 00:00:10 (PAT).

ACCT and APAT are identical 1Hz timescales, but since the definitions of 
the origins of NTP, 1588/PTP, and Unix/POSIX timescales are stated in 
terms of TAI or UTC,  ACCT and APAT are defined in terms of CCT and PAT 
to retain the distinction.

Leap Seconds are renamed Earth Corrections. Earth Corrections behave 
identically to Leap Seconds after 1972-01-01T00:00:00Z (UTC) = 
1972-01-01 00:00:10 (TAI), or 1972-01-01T00:00:00Z (CCT) = 1972-01-01 
00:00:10 (PAT). Prior to 1972, Earth Corrections are artificially 
applied to properly adjust the alignment of the NTP and Unix/POSIX 
origins to 1972-01-01T00:00:00Z (CCT).

The legend, table, and diagram below summarize the design of the CCT 
timescales.

CCT  - Common Calendar Time (Coordinated Universal Time (UTC) after 
1972-01-01T00:00:00Z(UTC))
ACCT - Anterior Common Calendar Time (1Hz scale before 
1972-01-01T00:00:00Z(CCT))
PAT  - Proper Atomic Time (International Atomic Time (TAI) after 
1972-01-01 00:00:10(TAI))
APAT - Anterior Proper Atomic Time (1Hz scale before 1972-01-01 
00:00:10(PAT))
EC   - Earth Correction (formerly "Leap Seconds")

----------------------------------------------------------------------------------------
Origin      |  CCT1972    | Coincides  |       ACCT        | Earth  

|      APAT

Name        |  Seconds    | with       | |Correction|
             |  Offset     | Origin of  |       CCT            | 

|         PAT

----------------------------------------------------------------------------------------
ACCT1900    | -2272060800 | NTP        | 1900-01-01T00:00:00Z | 10 | 
1900-01-01 00:00:10
APAI1958    |  -441763210 | TAI        | 1957-12-31T23:59:50Z | 10 | 
1958-01-01 00:00:00
APAT1970    |   -63072010 | 1588/PTP   | 1969-12-31T23:59:50Z | 10 | 
1970-01-01 00:00:00
ACCT1970    |   -63072000 | Unix-POSIX | 1970-01-01T00:00:00Z | 10 | 
1970-01-01 00:00:10
APAT1972    |         -10 | TAI1972-10 | 1971-12-31T23:59:50Z | 10 | 
1972-01-01 00:00:00
PAT1972     |           0 | TAI1972    | 1972-01-01T00:00:00Z | 10 | 
1972-01-01 00:00:10 CCT1972     |           0 | UTC1972    | 
1972-01-01T00:00:00Z | 10 | 1972-01-01 00:00:10
CCT1972_7_1 |   +15724800 | First Leap | 1972-07-01T00:00:00Z | 11 | 
1972-07-01 00:00:11
CCT1980_1_6 |  +252892800 | GPS Epoch  | 1980-01-06T00:00:00Z | 19 | 
1980-01-06 00:00:19
----------------------------------------------------------------------------------------

----------------------------------------------------------------------------
            TAI
         APAT1958
   1958-01-01 00:00:00
             |       1588/PTP
             |       APAT1970
             | 1970-01-01 00:00:00
             |         |                PAT1972
             |         |        1972-01-01 00:00:10 TAI
             |         |                   |
APAT - - - -|- - - - -|- - - - - - - - - <|>---------------------------- 
PAT
       -441763210  -63072010               0
                                           |
EC 10 10 10 10 10 10 10 10 10 10 10 10 10 10 10 10 10 10 11 11 11 11 19  EC
       |                 |                 |              |
  -2272060800       -63072000              0          +15724800 +252892800
ACCT -|- - - - - - - - -|- - - - - - - - <|>-------------|-----------|-- CCT
       |                 |                 | |           |
       |                 |              CCT1972 |           |
       |                 |    1972-01-01T00:00:00Z UTC |           |
       |              POSIX                        First Leap Second  |
       |             ACCT1970 CCT1972_7_1     |
       |      1970-01-01T00:00:00Z 1972-07-01T00:00:00Z   |
      NTP GPS Epoch
   ACCT1900 CCT1980_1_6
1900-01-01T00:00:00Z 1980-01-06T00:00:00Z
----------------------------------------------------------------------------

Comments welcome.

-Brooks
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