diff --git a/doc/RTD/source/ParameterFiles/output_selection.rst b/doc/RTD/source/ParameterFiles/output_selection.rst
index 3ec69485d175e9c295e9883125e920e687c66453..8100c97abdc8f2839cffa29c9683bcf68bea00f0 100644
--- a/doc/RTD/source/ParameterFiles/output_selection.rst
+++ b/doc/RTD/source/ParameterFiles/output_selection.rst
@@ -49,14 +49,32 @@ final time is specified in the list.
Output Selection
~~~~~~~~~~~~~~~~
-With SWIFT, you can select the particle fields to output in snapshot
-using the parameter file. In section ``SelectOutput``, you can remove
-a field by adding a parameter formatted in the following way
-``field_parttype`` where ``field`` is the name of the field that you
-want to remove (e.g. ``Masses``) and ``parttype`` is the type of
-particles that contains this field (e.g. ``Gas``, ``DM`` or ``Star``).
-For a parameter, the only values accepted are 0 (skip this field when
-writing) or 1 (default, do not skip this field when writing). By
+Users can generate a ``yaml`` file containing all the possible fields
+available for a given configuration of SWIFT by running
+``./swift --output-params output.yml`` or equivalently ``./swift -o
+output.yml``. The file generated contains the list of fields that a
+simulation running with this config would output in each snapshot. It
+also lists the description string of each field and the unit
+conversion string to go from internal comoving units to physical
+CGS. Entries in the file look like:
+
+.. code:: YAML
+
+ SelectOutput:
+ # Particle Type Gas
+ Coordinates_Gas: 1 # Co-moving positions of the particles. ::: Conversion to physical CGS: a U_L [ cm ]
+ Velocities_Gas: 1 # Peculiar velocities of the stars. This is (a * dx/dt) where x is the co-moving positions of the particles. ::: Conversion to physical CGS: U_L U_t^-1 [ cm s^-1 ]
+ Masses_Gas: 1 # Masses of the particles. ::: Conversion to physical CGS: U_M [ g ]
+ SmoothingLengths_Gas: 1 # Co-moving smoothing lengths (FWHM of the kernel) of the particles. ::: Conversion to physical CGS: a U_L [ cm ]
+
+Users can select the particle fields to output in snapshot using the
+YAML parameter file. In section ``SelectOutput``, users can demand to
+remove a field by adding a parameter formatted in the following way
+``field_parttype`` where ``field`` is the name of the field that is to
+be removed (e.g. ``Masses``) and ``parttype`` is the type of particles
+that contains this field (``Gas``, ``DM``, ``Stars`` or ``BH``). For
+a parameter, the only values accepted are ``0`` (skip this field when
+writing) or ``1`` (default, do not skip this field when writing). By
default all fields are written.
This field is mostly used to remove unnecessary output by listing them
@@ -64,10 +82,12 @@ with 0's. A classic use-case for this feature is a DM-only simulation
(pure n-body) where all particles have the same mass. Outputting the
mass field in the snapshots results in extra i/o time and unnecessary
waste of disk space. The corresponding section of the ``yaml``
-parameter file would look like this::
+parameter file would look like:
+.. code:: YAML
+
SelectOutput:
Masses_DM: 0
-You can generate a ``yaml`` file containing all the possible fields
-available for a given configuration of SWIFT by running ``./swift --output-params output.yml``.
+Entries can simply be copied from the ``output.yml`` generated by the
+``-o`` runtime flag.
diff --git a/doc/RTD/source/ParameterFiles/parameter_description.rst b/doc/RTD/source/ParameterFiles/parameter_description.rst
index 93b85311b0d07d432ffdd7338bf68b7b3afe8cbe..08543367b0e6ba4361d025c3c2cfe93c9c7fbe9c 100644
--- a/doc/RTD/source/ParameterFiles/parameter_description.rst
+++ b/doc/RTD/source/ParameterFiles/parameter_description.rst
@@ -692,10 +692,12 @@ using the parameter:
The default level of ``0`` implies no compression and values have to be in the
range :math:`[0-9]`. This integer is passed to the i/o library and used for the
-loss-less GZIP compression algorithm. Higher values imply higher compression but
-also more time spent deflating and inflating the data. Note that up until HDF5
-1.10.x this option is not available when using the MPI-parallel version of the
-i/o routines.
+loss-less GZIP compression algorithm. The compression is applied to *all* the
+fields in the snapshots. Higher values imply higher compression but also more
+time spent deflating and inflating the data. When compression is switched on
+the SHUFFLE filter is also applied to get higher compression rates. Note that up
+until HDF5 1.10.x this option is not available when using the MPI-parallel
+version of the i/o routines.
Finally, it is possible to specify a different system of units for the snapshots
than the one that was used internally by SWIFT. The format is identical to the
diff --git a/doc/RTD/source/Snapshots/index.rst b/doc/RTD/source/Snapshots/index.rst
index f1466eec18bf2625d1dfc3aff75f1e40a96b5ebc..3510e2e1369af067c99c3935fd622cdca65bc834 100644
--- a/doc/RTD/source/Snapshots/index.rst
+++ b/doc/RTD/source/Snapshots/index.rst
@@ -165,7 +165,20 @@ The last column in the table gives the ``enum`` value from ``part_type.h``
corresponding to a given entry in the files.
Each group contains a series of arrays corresponding to each field of the
-particles stored in the snapshots.
+particles stored in the snapshots. The exact list of fields depends on what
+compile time options were used and what module was activated. A full list can be
+obtained by running SWIFT with the ``-o`` runtime option (See
+:ref:`Output_selection_label` for details). Each field contains a short
+description attribute giving a brief summary of what the quantity represents.
+
+All the individual arrays created by SWIFT have had the Fletcher 32 check-sum
+filter applied by the HDF5 library when writing them. This means that any
+eventual data corruption on the disks will be detected and reported by the
+library when attempting to read the data.
+
+Additionally, some compression filter may have been applied to the fields. See
+the :ref:`Parameters_snapshots` section of the parameter file description for
+more details.
Unit information for individual fields
--------------------------------------
diff --git a/examples/parameter_example.yml b/examples/parameter_example.yml
index e9963a631a8f703d6574bd76336a4adf18f87a30..ddec176922c7f6449acb571cb91be2d0893f7a5d 100644
--- a/examples/parameter_example.yml
+++ b/examples/parameter_example.yml
@@ -132,7 +132,7 @@ Snapshots:
time_first: 0. # (Optional) Time of the first output if non-cosmological time-integration (in internal units)
delta_time: 0.01 # Time difference between consecutive outputs (in internal units)
invoke_stf: 0 # (Optional) Call VELOCIraptor every time a snapshot is written irrespective of the VELOCIraptor output strategy.
- compression: 0 # (Optional) Set the level of compression of the HDF5 datasets [0-9]. 0 does no compression.
+ compression: 0 # (Optional) Set the level of GZIP compression of the HDF5 datasets [0-9]. 0 does no compression. The lossless compression is applied to *all* the fields.
distributed: 0 # (Optional) When running over MPI, should each rank write a partial snapshot or do we want a single file? 1 implies one file per MPI rank.
int_time_label_on: 0 # (Optional) Enable to label the snapshots using the time rounded to an integer (in internal units)
UnitMass_in_cgs: 1 # (Optional) Unit system for the outputs (Grams)