Update data-products.rst

docs/data-products.rst

@@ -421,17 +421,22 @@ corners.
 
 Initial Conditions
 ------------------
-The initial density fields are saved at two resolutions, 576<sup>3</sup>
-and 1152<sup>3</sup>.  The resulting particle displacements under the
+The initial density fields are saved at two resolutions, 576\ :sup:`3`
+and 1152\ :sup:`3`.  The resulting particle displacements under the
 Zel'dovich approximation are also saved (Abacus applies 2LPT on-the-fly,
 so the files only contain ZA).  For the covariance suite of 500 Mpc/*h* boxes,
 only the lower resolution is available.
 
 The ICs are saved in ASDF files and should have a discoverable data structure.
-In addition to the usual parameter set, a set of growth factors D(*z*)/D(*z*<sub>init</sub>)
+In addition to the usual parameter set, a set of growth factors D(*z*)/D(*z*\ :sub:`init`)
 are saved as the parameter name ``GrowthTable``.  The input linear power spectrum
 is also saved in the file.
 
 Late-time particle samples (e.g. from halo catalogs) can be connected to their
 location in the ICs via the PID.  Pass ``lagr_pos`` or ``lagr_idx`` to the ``unpack_bits``
 parameter of ``CompaSOHaloCatalog``, or to the ``load`` parameter of ``abacusnbody.data.read_abacus.read_asdf``.
+
+The initial density field is in units of fractional overdensity at *z*\ :sub:`init`.
+The ``[0,0,0]`` element of the field is at location ``(x,y,z)=(-0.5,-0.5,-0.5)``, in units
+where the box length is 1 and following the Abacus convention of zero-centered domain.
+