How long can your clock hold?

Pick an oscillator and an outage length, and see how far your time drifts once GNSS is gone.

LIVE DEMO · HOLDOVER

IN TOLERANCE

Chart of time error against hours since GNSS loss for three oscillator types, showing the TCXO and OCXO curves crossing a dashed example budget line while the rubidium curve stays below it.
  • time error
  • tolerance
  • outage length

Illustrative

CONTROLS

1 h
1 µs
TIME ERROR
± 0.4 µs
IN TOLERANCE FOR
Whole outage
STATUS
In tolerance

Simulated, with illustrative figures. Runs in your browser; nothing is uploaded.

Assumptions behind the figures
  • Time error x(t) = x0 + y0·t + ½·D·t², starting at x0 = 0, with the offset y0 and ageing D in the same direction (worst case)
  • TCXO: y0 = 1×10⁻⁸, ageing 1×10⁻⁹ per day
  • OCXO: y0 = 1×10⁻¹⁰, ageing 5×10⁻¹¹ per day
  • Rubidium: y0 = 1×10⁻¹², ageing 3×10⁻¹³ per day
  • Temperature swings: ±10 K over 24 h with an assumed sensitivity for each oscillator

HOW IT WORKS

Lock, coast, drift

  1. Lock

    With GNSS, the clock is steered to satellite time.

  2. Coast

    When GNSS drops out, the oscillator runs alone and slowly drifts.

  3. Tolerance

    How long it stays inside your limit depends on its quality and its temperature.

TRY THIS

Things to try

  • Swap a TCXO for a rubidium clock and compare
  • Turn on temperature swings
  • Set your own tolerance and find the hold time
  • Try a week-long outage

MORE

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LIVE DEMO

Spot the spoof

Watch a position get dragged away, and which checks catch it.