Time¶
The time side of every variable: how far a recorded time can be from when the thing it describes happened. Accuracy: the clock that made the stamp drifts and is corrected in jumps, and the value often describes a window that ended before its stamp. Resolution: the grid the stamp sits on, and the width of the interval one value stands for.
The working reference¶
The working reference is SNUADC stamp-model time: the SNUADC sample clock, placed on the recorder PC's timeline by the stamp model (drift and corrections fitted, the signal lost at each correction added back). Every delay in the planner is measured against it. Its own error against the PC is a few milliseconds where the SNUADC's corrections are seen; in recordings that make no SNUADC correction it rests on the port's typical rate and can drift by about ±0.1 s per hour (Long SNUADC recordings with no correction at all). The PC's error against UTC is assumed.
Every clock's route to UTC passes through Recorder PC against UTC, assumed. That shared link sets the absolute accuracy of every time in the dataset alike, so it cancels whenever times are compared with each other, which is what synchronising variables needs. The table therefore follows each clock to the working reference instead; each clock's page also draws its full route to UTC.
Clocks¶
Every clock in the dataset, how it is linked to the working reference (a traceability chain: only as strong as its weakest link), and how many variables it stamps or spaces. Each clock's page lists its links to other clocks.
| Clock | Type | Route to the working reference | Variables |
|---|---|---|---|
| BIS clock | oscillator | 1 link, weakest measured | 2 |
| CardioQ clock | oscillator | 1 link, weakest measured | 1 |
| Hospital records clock | software | 2 links, weakest assumed | 44 |
| Monitor analogue output clock | oscillator | 1 link, weakest estimated | 0 |
| Pacemaker clock | oscillator | 1 link, weakest measured | 0 |
| Primus clock | oscillator | 2 links, weakest measured | 2 |
| Pulse oximeter frame clock | oscillator | 1 link, weakest measured | 0 |
| Recorder PC clock | software | 1 link, weakest measured | 20 |
| SNUADC sample clock | oscillator | the working reference | 3 |
| Solar8000 clock | unknown | 1 link, weakest measured | 0 |
| UTC | reference | — (outside the release) | 0 |
Every time stamp: accuracy and resolution¶
Each kind of time stamp in the dataset, placed by how far it lies after the end of the interval its value describes, against the working reference (across), and by how wide that interval is (up). Drawn from the atlas data each time the site is built, so it follows every update; the same data drives the synchronisation planner.
Plan a multi-variable analysis¶
The synchronisation planner takes the variables an analysis combines and reports how well their times line up, how we know, and what window sizes keep cross-modal features meaningful.
The devices that keep the clocks and produce the variables have pages of their own.