Comparing with other monitors
Lay another monitor's record of the same blast over this one, placed on the blast's clock and turned by its own frame, with its peak, frequency and arrival.
A blast is often recorded by several monitors at different distances and bearings. On an event linked to a blast, the analyser can lay another monitor's record of the same blast over this one, as one more dataset: placed on the blast's clock, turned by its own unit's frame, and compared figure by figure with this record.
Comparing records is part of Event Compare, one of your team's beta features. It is by invitation: an owner or admin of your team asks for it under Settings, in Beta features. Until it is on, Compare with… is not offered.
Open another monitor's record
On a ViB event linked to a blast, click Compare with… under the charts. Under the blast's seismograph records, Other monitors on this blast lists every other unit's record of the blast that you can see, each with its unit and its distance from the blast. Tick one to lay it over this record, and untick it to take it away. A record that has not been analysed is listed as Not analysed yet. This unit's own other records are not listed: they are not other monitors.
The legend under the charts then names each dataset. Click one to hide it; Alt-click one to show only that one. The page's link carries the records you are comparing, so whoever opens it sees the same.
In the Visualiser, Analyse together in the line-up opens the analyser with the records you picked already laid over the primary. See Comparing monitors.
How it is placed
Each record of a blast has a place on the blast's clock. The other monitor's record is laid on this record's time axis at the gap between the two places: a unit whose record triggered 40 ms later is drawn 40 ms to the right.
The chip under the charts says how the pair was placed, how sure that is, and the offset in seconds. It names the weaker of the two records' methods, since the offset is only as good as the placement it rests on. Best first:
| Chip | The weaker of the two records was |
|---|---|
| GNSS with timing pulses | Marked on GPS time, with the timing pulses that measure the true sample rate |
| GNSS trigger mark | Marked on GPS time with no pulses, so read at its nominal sample rate |
| From the arrival | Placed by its first motion against the arrival the plan predicts |
| Placed by hand | Placed by a person |
| Device clock only, laid trigger on trigger | Not placed: its unit's clock is too coarse |
| Laid trigger on trigger | Not placed, with nothing to place it by |
The ± is on the gap between the two records, at about one standard deviation: each record's own error, combined. Two GNSS records share the error of their group's place on the blast's clock, which cancels between them, so their ± is about a sample. A pair placed from first arrivals is typically good to tens of milliseconds.
Laid trigger on trigger means the other record's trigger is put on this record's trigger. That says nothing about when either unit's ground moved, so read the traces side by side for their shapes and sizes, not their timing. How each method works: The blast's clock.
How it is drawn
Another unit's X, Y and Z are its own axes, not this unit's, so its channels never pair with this record's as written. It is drawn one of two ways:
- By component, when this record reads T V L and both units' orientation resolves. The other record is turned by its own frame into its own Tran, Vert and Long, each relative to the blast from where it stood, and each component is compared with this record's. This unit's rotation is never applied to the other unit.
- As its vector sum otherwise. The peak vector sum does not depend on how either unit was lying, so it always compares.
The line under the charts says what would compare them component by component. Switch to T V L to compare component by component appears when that switch would draw more by component, one click. When the other unit's orientation does not resolve, it says so: open that unit's own event and resolve it there. See Frames and orientation.
What the row says
Under the charts, a row headed with the other unit's name (vs and its label) gives:
- the difference in PVS, the peak vector sum, always;
- the difference for Tran, Vert and Long, when the two are drawn by component;
- this record's dominant frequency against the other's;
- when the other record's ground began to move against this one's: arrives … ms later or arrives … ms earlier.
Every difference is this record's figure against the other's, as a share of the other's: −40 % means this record read 40 % less. In the full-screen workspace the same figures are in the Readings tab.
The arrival reads arrival: not on one clock when either record is not placed on the blast's clock, or when either record's first motion could not be found.
What the arrival difference is not: where a record was placed from its first arrival, its first motion was put where the plan predicts, so between two such records the difference restates the plan's prediction for their two distances. It is measured, not predicted, only between two GNSS records.
Nudge the offset
Adjust, on the chip, moves the other record along the time axis: the arrow keys move it one sample, and Shift with an arrow moves ten. The chip shows the offset in seconds and the samples moved as you go, and reads Adjusted here, not saved while the record is off its placement. The arrival difference follows the nudge.
Reset, or Esc, puts the record back on its placement.
Save, or Enter, keeps the other record where you laid it against this one, if you can edit the project's blasts, both records are linked to the blast (a suggested link is not enough), and this record is placed on the blast's clock (a record laid on its own clock gives the other nowhere to stand). The blast is placed again shortly after: the other record is then Placed by hand, so many milliseconds after this record, and stays that far from it whenever the blast is placed again, wherever this record moves (see Placed by hand). The ± saved with it is one sample of the coarser of the two records, the finest step the chip moves by; the pair's ± then reads wider, since this record's own is added to it. A record cannot be placed against itself, nor against a record already placed against it. If the save is refused you are told why, and the nudge stays on screen.
The chip names the record a placement was saved against: Placed by hand against this record, or against another monitor by its name, such as Placed by hand against G4. Where it was saved against this record and you can edit the project's blasts, the chip also offers Clear saved placement, whether or not this record is placed on the blast's clock. The other record leaves its saved place at once and is laid on its own trigger until the blast is placed again, shortly after, by the usual rules. Its new place shows once the blast has been placed again, the next time you open the page. If the clear is refused you are told why, and the saved placement is put back. One saved against another record is cleared on that record's page.
Where you cannot save, the chip offers Done instead: it keeps the nudge for what you are looking at, and it is gone when you leave the page. Either way, a nudge lines up by eye; treat any timing read from it with the care its ± asks.
In the Visualiser's analyser, the records laid over the primary cannot be adjusted.