One instant. Two integers. A named time scale.

Decimal seconds since J2000.0

833630400.1234567890 s

TT calendar label

2026-06-02 00:00:00.123456789 TT

UTC label

2026-06-01 23:58:50.939456789 UTC

The value of a timecode is exactly seconds + ticks / 10¹⁰. It is a representation, not a measurement: how well any clock knows the time is a separate question.

Most timestamp formats leave something implicit: the time scale, the zone, how many fractional digits mean what, or what happens when arithmetic runs off the end. UTP's case is that all of those can be fixed in the contract, so that two independent implementations reading the same string reach the same instant and the same arithmetic result.

1. The scale is part of the format

   Every UTP timestamp counts TT, and its marker says which contract applies. There is no local offset to guess and no discontinuity to skip: one second of count is one SI second.

   J2000.0 0:0000000000 UTP
   in UTC  11:58:55.816

2. Exact integers on a fixed grid

   Representable instants on the 100 ps grid are held exactly by a pair of integers; conversions from floating-point inputs such as Julian Date or POSIX time round to the nearest tick, ties to even. Normalization carries and borrows with floor division, and a result outside the 64-bit range is an error, never a wrap, clamp, or saturation.

   normalize(100, −1)
     → (99, 9999999999)
   normalize(0, −25000000000)
     → (−3, 5000000000)

3. One canonical spelling

   The emitter always writes the ten-digit suffix form. The parser accepts that and the documented prefix form, nothing looser: a shortened tick field could be read as left- or right-padded, so it is rejected rather than guessed.

   accepted 0:5000000000 UTP
   rejected 0:5 UTP

4. Decimal precision you can project

   Because a tick is a power of ten, reducing to seconds, milliseconds, microseconds or nanoseconds is a decimal shift with half-to-even rounding and a stated error bound. The canonical value is never replaced by its projection.

   full 0.2500000000
   ms   0.250

5. Order and storage that behave

   Sorting by (seconds, ticks) is chronological. Both fields fit 64-bit integer columns; 32-bit types are ruled out because ticks reach past 2³².

   CHECK (utime_ticks
     BETWEEN 0 AND 9999999999)

6. Agreement you can test

   The draft includes language-neutral test vectors for formatting, parsing, normalization and projection, derived from the specification rather than from any one implementation. Cross-language conformance is the goal, and still work in progress. The marker spelling shown here is proposed; reference parsers and test vectors have not yet migrated.

   (833630400, 1234567890)
     → "833630400:1234567890 UTP"

Strict parsing, by example

UTP separates what is stored from how it is shown. The stored value is a single count; each civil label is derived from it with whatever rules that view needs.

The core protocol represents universal instants. True Local Time is a separate, related proposal for longitude-based local clocks without time zones or seasonal clock changes; this draft does not specify or implement it, though a later version might. Calendar design is separate work too. The zone labels below only show that today's civil rules can still be applied as views.

A tick is the smallest step the encoding can name. In one tick, light travels 2.99792458 cm. That says nothing about how well a given clock knows the time: an internet-synchronized computer is typically good to milliseconds. UTP lets each consumer project to the precision it actually has.

Projections are for display and downstream consumers. Only the full tier round-trips exactly; arithmetic belongs on the canonical pair.

The draft specifies how a UTP timestamp relates to the scales people already use. Some relations are constant and exact. UTC is not: its offset from atomic time has changed over the decades, so every conversion depends on the date.

At its 28th meeting in October 2026, the General Conference on Weights and Measures adopted Resolution 5: continuous UTC takes effect on 20 May 2027, with the difference |UT1 − UTC| allowed to reach 3 600 s. The resolution sets a limit, not a scheduled correction.

For UTP this settles a question of emphasis. Avoiding future leap seconds is no longer a reason to choose it; the case rests on the representation and operation contract above. The leap seconds already in the record remain, so historical conversion still needs the table.

UTP is a research draft. Its specification and test vectors are not yet published, and details may change before 1.0.0.

Where to go from here

• Read a timecode field by field§1
• See how one instant becomes many clocks§3
• Check the conversion rules§5