.. index:: plotting Declares which :ref:`NXdata` (or :ref:`NXsubentry`) group contains the data to be shown by default. It is needed to resolve ambiguity when more than one :ref:`NXdata` group exists. The value is the name of the default :ref:`NXdata` group. It is recommended (as of NIAC2014 [#]_) to use this attribute to help define the path to the default dataset to be plotted. .. [#] NIAC2014 discussion summary: http://wiki.nexusformat.org/2014_How_to_find_default_data (**required**) :ref:`NXentry` describes the measurement. The top-level NeXus group which contains all the data and associated information that comprise a single measurement. It is mandatory that there is at least one group of this type in the NeXus file. The data group .. note:: Before the NIAC2016 meeting [#]_, at least one :ref:`NXdata` group was required in each :ref:`NXentry` group. At the NIAC2016 meeting, it was decided to make :ref:`NXdata` an optional group in :ref:`NXentry` groups for data files that do not use an application definition. It is recommended strongly that all NeXus data files provide a NXdata group. It is permissable to omit the NXdata group only when defining the default plot is not practical or possible from the available data. For example, neutron event data may not have anything that makes a useful plot without extensive processing. Certain application definitions override this decision and require an :ref:`NXdata` group in the :ref:`NXentry` group. The ``minOccurs=0`` attribute in the application definition will indicate the :ref:`NXdata` group is optional, otherwise, it is required. .. [#] NIAC2016: http://wiki.nexusformat.org/NIAC2016, https://github.com/nexusformat/NIAC/issues/16 ISIS Muon IDF_Version Extended title for entry Unique identifier for the experiment, defined by the facility, possibly linked to the proposals Brief summary of the experiment, including key objectives. Description of the full experiment (document in pdf, latex, ...) User or Data Acquisition defined group of NeXus files or NXentry Brief summary of the collection, including grouping criteria. unique identifier for the measurement, defined by the facility. Reserved for future use by NIAC. See https://github.com/nexusformat/definitions/issues/382 (alternate use: see same field in :ref:`NXsubentry` for preferred) Official NeXus NXDL schema to which this entry conforms. This field is provided so that :ref:`NXentry` can be the overlay position in a NeXus data file for an application definition and its set of groups, fields, and attributes. *It is advised* to use :ref:`NXsubentry`, instead, as the overlay position. NXDL version number URL of NXDL file Local NXDL schema extended from the entry specified in the ``definition`` field. This contains any locally-defined, additional fields in the entry. NXDL version number URL of NXDL file Starting time of measurement Ending time of measurement Duration of measurement Time transpired actually collecting data i.e. taking out time when collection was suspended due to e.g. temperature out of range Such as "2007-3". Some user facilities organize their beam time into run cycles. Name of program used to generate this file Program version number configuration of the program Revision id of the file due to re-calibration, reprocessing, new analysis, new instrument definition format, ... This is the flightpath before the sample position. This can be determined by a chopper, by the moderator or the source itself. In other words: it the distance to the component which gives the T0 signal to the detector electronics. If another component in the NXinstrument hierarchy provides this information, this should be a link. Notes describing entry A small image that is representative of the entry. An example of this is a 640x480 jpeg image automatically produced by a low resolution plot of the NXdata. The mime type should be an ``image/*``