Add how to specify when there is no clock sync information

[WayneCrawford]

Also cover case where data are corrected, but you don't know the values used. In my opinion, you should use the same nomenclature in StationXML as when you don't have drift correction calculated.

[WayneCrawford]

I propose to put null (not 'null'!) in the appropriate fields of the Clock Correction comment, so the nominal Comment would be:

<Comment subject=”Clock Correction”><Value>“{drift: {type: piecewise_linear,
 syncs_instrument_reference: [['2016-09-10T00:00:00Z', null],
 ['2017-01-12T00:00:01Z', null]]}}”</Value></Comment>

where the instrument "syncs" are the instrument start and end times? Or simply

<Comment subject=”Clock Correction”><Value>“{drift: {type: piecewise_linear,
 syncs_instrument_reference: [[null, null],
 [null, null]]}}”</Value></Comment>

or

<Comment subject=”Clock Correction”><Value>“{drift: {type: piecewise_linear,
 syncs_instrument_reference: null}}”</Value></Comment>

?or even?

<Comment subject=”Clock Correction”><Value>“{drift: null}”</Value></Comment>

[WayneCrawford]

The last is very clean, but could be misinterpreted as indicating that there is no clock drift (which actually should be indicated by having identical instrument and sync datestrings within each syncs_instrument_reference element).

[joelsimon]

I prefer the last, but I also fear null could be misinterpreted as, e.g., 0.

What about simply an empty element, like in StationXML when the response is unknown/undefined?

<Comment subject="Clock Correction”><Value></Value></Comment>

As StationXML puts it [adapted], "...to positively indicate that no [clock correction] exists." (pg. 62 of v1.2 specification)

(I know that's response and not drift spec from StationXML, but it seems sensible to me to apply it here?)

[WayneCrawford]

@jcarter also thinks that there should be no value provided (rather than null) when there is no/missing clock drift information.

How to do that while retaining existing structure? Or at least one that's not too heavy?

One "stupid" option (more w.r.t. JSimon's question) would be to allow "0" as an alternative to null: anything that is not a date means that we have no measurement.

[WayneCrawford]

The last three examples I presented (all with all null values) can all be replaced by:

<Comment subject=”Clock Correction”><Value></Value></Comment>

But what to do for cases where at least one synchronizationvalue is non-null? For example, when we know the starting synchronization but not the ending.
Or when we measured the GPS clock time correponding to a second pulse from the instrument, but don't know which second it was on the instrument?

I suppose this information could be stored in a subnetwork file, but the StationXML file would simply indicate the above, meaning that there is no accurate clock correction to apply/applied

[WayneCrawford]

Standards document modified to include:

If no drift is measured
Specify:

<Comment subject=”Clock Correction”><Value></Value></Comment>

This means that there is a clock drift, but we don’t know what it is.

We deliberately do not include information about the time base, for clarity and because the Nominal Clock Drift field could be misinterpreted as the actual drift

[KaseyAderhold]

Not that I necessarily agree or prefer it, but if following StationXML nomenclature wouldn't we use zero? e.g. https://docs.fdsn.org/projects/stationxml/en/latest/reference.html#correction-required: "A value of zero indicates no correction was applied."

[WayneCrawford]

After discussion, we decided to use the nomenclature I specified in my May 10th comment

[WayneCrawford]

The problem with the proposed solution:

<Comment subject=”Clock Correction”><Value></Value></Comment>

is that it does not indicate that it concerns drift (leapsecond has the same subject)

Two possible solutions are:

1. Include the "drift" element, with an empty sub-dict

   <Comment subject=”Clock Correction”><Value>{drift: {}}</Value></Comment>

2. Change the subject from "Clock Correction" for drift and leapseconds to "Clock Drift" for the former and "Leapseconds" for the latter.

   <Comment subject=”Clock Drift”><Value></Value></Comment>

Any preferences?

[jac5796]

Second option seems cleaner J ************************************************************ John A. Collins Dept. of Geology and Geophysics, MS 24 Woods Hole Oceanographic Institution 360 Woods Hole Road Woods Hole, MA 02543 e-mail: ***@***.*** voice: +1-508-289-2733 **********************************************

…

On Sep 1, 2025, at 05:35, Wayne Crawford ***@***.***> wrote: WayneCrawford left a comment (FDSN/OBS-standards#42) <https://nam02.safelinks.protection.outlook.com/?url=https%3A%2F%2Fgithub.com%2FFDSN%2FOBS-standards%2Fissues%2F42%23issuecomment-3241618799&data=05%7C02%7Cjcollins%40whoi.edu%7C47a6907ab2884d55135508dde93ae233%7Cd44c5cc6d18c46cc8abd4fdf5b6e5944%7C0%7C0%7C638923161301894364%7CUnknown%7CTWFpbGZsb3d8eyJFbXB0eU1hcGkiOnRydWUsIlYiOiIwLjAuMDAwMCIsIlAiOiJXaW4zMiIsIkFOIjoiTWFpbCIsIldUIjoyfQ%3D%3D%7C0%7C%7C%7C&sdata=0RONpVcdU4JimJQd%2BCBh8N3RraFOEb%2B06r1abVUPEvo%3D&reserved=0> The problem with the proposed solution: <Comment subject=”Clock Correction”><Value></Value></Comment> is that it does not indicate that it concerns drift (leapsecond has the same subject) Two possible solutions are: Include the "drift" element, with an empty sub-dict <Comment subject=”Clock Correction”><Value>{drift: {}}</Value></Comment> Change the subject from "Clock Correction" for drift and leapseconds to "Clock Drift" for the former and "Leapseconds" for the latter. <Comment subject=”Clock Drift”><Value></Value></Comment> Any preferences? — Reply to this email directly, view it on GitHub <https://nam02.safelinks.protection.outlook.com/?url=https%3A%2F%2Fgithub.com%2FFDSN%2FOBS-standards%2Fissues%2F42%23issuecomment-3241618799&data=05%7C02%7Cjcollins%40whoi.edu%7C47a6907ab2884d55135508dde93ae233%7Cd44c5cc6d18c46cc8abd4fdf5b6e5944%7C0%7C0%7C638923161301915037%7CUnknown%7CTWFpbGZsb3d8eyJFbXB0eU1hcGkiOnRydWUsIlYiOiIwLjAuMDAwMCIsIlAiOiJXaW4zMiIsIkFOIjoiTWFpbCIsIldUIjoyfQ%3D%3D%7C0%7C%7C%7C&sdata=7zlG4AePUUubPuTsCr3WE46R6jUBeOdqh8vcKzJsXWQ%3D&reserved=0>, or unsubscribe <https://nam02.safelinks.protection.outlook.com/?url=https%3A%2F%2Fgithub.com%2Fnotifications%2Funsubscribe-auth%2FACEP43Y2R2DDAVC5GI76AQT3QQHN5AVCNFSM6AAAAABVJDN4AKVHI2DSMVQWIX3LMV43OSLTON2WKQ3PNVWWK3TUHMZTENBRGYYTQNZZHE&data=05%7C02%7Cjcollins%40whoi.edu%7C47a6907ab2884d55135508dde93ae233%7Cd44c5cc6d18c46cc8abd4fdf5b6e5944%7C0%7C0%7C638923161301929665%7CUnknown%7CTWFpbGZsb3d8eyJFbXB0eU1hcGkiOnRydWUsIlYiOiIwLjAuMDAwMCIsIlAiOiJXaW4zMiIsIkFOIjoiTWFpbCIsIldUIjoyfQ%3D%3D%7C0%7C%7C%7C&sdata=T8f%2BY6pDCnNmuY0TXHkx6UphL17wr6mmECIYuJQXLu4%3D&reserved=0>. You are receiving this because you are subscribed to this thread.