[Nexus] Question about start_time field

[Pete Jemian]

This is a great question.  NeXus has not made such a distinction yet in the use of this field.  As you say, often the start of an acquisition and the start of the actual measurement are nearly synchronous.

I agree 100% with Filipe.  You can write BOTH times if you wish, though,  The _other_ time could be recorded as an additional field with the same format (but this would be your choice) using a more descriptive field name, such as `start_time_button_pressed`.

Pete

On 7/9/2021 2:38 AM, Filipe Maia via NeXus wrote:
> Hi Henrik,
> 
> I think setting it to when the actual scan starts is the more logical choice.
> 
> Cheers,
> Filipe
> 
> On Fri, 9 Jul 2021 at 09:33, Henrik Enquist via NeXus <nexus at shadow.nd.rl.ac.uk <mailto:nexus at shadow.nd.rl.ac.uk>> wrote:
> 
>     Hi,
> 
>     We are looking at the nexus output of Sardana, and a question came up about the exact meaning of scan_start.
> 
>     https://manual.nexusformat.org/classes/applications/NXscan.html#nxscan-entry-start-time-field <https://manual.nexusformat.org/classes/applications/NXscan.html#nxscan-entry-start-time-field>
> 
> 
>     We have the choice of setting it to the exact time when the user started the scan macro, or when the actual scan starts. The documentation linked above does not mention any details. In many cases these two will be so close that it doesn't make any practical difference. But if for example a large prescan snapshot is taken, then they can be a number of seconds apart.
> 
> 
>     So the question is, which time should we put in the start_time? The time when the user pressed the button, or the time when the scan started running?
> 
> 
>     I tried sending this yesterday but I probably did it a little too early, before my registration on the list was completed. Sorry if this causes any noise.
> 
> 
>     Cheers,
> 
>     Henrik
> 
> 
> 
>     ----
>     Dr. Henrik Enquist
>     Control Software Engineer
>     MAX IV Laboratory
>     Fotongatan 2
>     221 00, Lund
>     Sweden
> 
>     Phone: +46 (0)272 15 45 45
>     Email: henrik.enquist at maxiv.lu.se <mailto:henrik.enquist at maxiv.lu.se>
>     Web: www.maxiv.lu.se <http://www.maxiv.lu.se>
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