Holdover test
How far does the time error go when GNSS is gone?
The operator pulls GNSS from a timing system, writes down the two times (removed, restored) and keeps the time-error record. Kshana splits the record at those times and measures each step against public ITU-T masks: the baseline while locked, the holdover, the recovery. It does not remove or restore anything, and it reads only the record. The scenario kind is holdover-test (docs/TIMING-HIL.md).
Measured against the mask, not conformance. The result is MODELLED: the step logic, the line fit and the recovery rule are checked on records built from formulas whose answers are known, and no laboratory holdover has been scored against an external oracle. The masks are transcribed from freely downloadable ITU-T Recommendations, and nothing here says that a clock or system meets, or is approved against, any Recommendation. The two times are the operator's statement and are not verified. The records in the two examples are generated for them; they are not measurements. Advisory software. Kshana is not type-approved navigation equipment (IEC 61108, IEC 61162) and not type-approved timing equipment.
kshana holdover-test.toml. The curve is drawn from the record the engine writes into it. Read here; nothing is uploaded.Opening the scenarios…
Verdict, step by step
Time error over the record
The three phases are shaded; the dashed vertical lines are the two times the operator stated. Dashed horizontal lines are the masks' limits on the maximum absolute time error, each drawn over the step its mask names, and the recovery band; a triangle marks when a budget or the ePRTC-A holdover envelope is first exceeded.
MTIE
Of the baseline and the holdover; a cross is a mask limit at the time its check was worst.
TDEV
The same two steps against the TDEV limits.
The numbers
Everything below is the engine's, in the units it states.
Mask checks
Each mask is measured on the step its condition names. A mask that needs a longer record than the step gave is INCOMPLETE, never extrapolated; every entry a Recommendation leaves for further study is absent.