Hi, Everybody! In order to ensure all my units are being done correctly, I have a field 'TE' that forces 'TotalEnergy' to be read off disk, like this: def _TE(field,data): return data.hierarchy.io.pop(data, 'TotalEnergy') lagos.add_field("TE", function=_TE, validators=[lagos.ValidateGridType()]) This lets me circumvent the assumptions that yt makes on a field by that name, specifically unit conversion. However, I can't seem to project it. I get the error, below. Does anyone have any ideas of either different ways to do this, or ways around the projection error? Thanks, d. Traceback (most recent call last): File "<stdin>", line 1, in <module> File "tmp.py", line 9, in <module> mp.plot() File "/home/dccollin/yt/uber.py", line 398, in plot fig = self.add_plots(field,axis,FirstOne) File "/home/dccollin/yt/uber.py", line 676, in add_plots **extra_args) File "/projects/lca-group/local-dev/lib/python2.6/site-packages/yt-2.0dev-py2.6-linux-x86_64.egg/yt/raven/plot_collection.py", line 719, in add_projection **field_parameters) File "/projects/lca-group/local-dev/lib/python2.6/site-packages/yt-2.0dev-py2.6-linux-x86_64.egg/yt/lagos/BaseDataTypes.py", line 1205, in __init__ self._refresh_data() File "/projects/lca-group/local-dev/lib/python2.6/site-packages/yt-2.0dev-py2.6-linux-x86_64.egg/yt/lagos/BaseDataTypes.py", line 237, in _refresh_data self.get_data() File "/projects/lca-group/local-dev/lib/python2.6/site-packages/yt-2.0dev-py2.6-linux-x86_64.egg/yt/lagos/BaseDataTypes.py", line 1380, in get_data self._get_dependencies(fields), self.hierarchy.io) File "/projects/lca-group/local-dev/lib/python2.6/site-packages/yt-2.0dev-py2.6-linux-x86_64.egg/yt/lagos/ParallelTools.py", line 1438, in _get_dependencies deps += ensure_list(fi[field].get_dependencies(pf=self.pf).requested) File "/projects/lca-group/local-dev/lib/python2.6/site-packages/yt-2.0dev-py2.6-linux-x86_64.egg/yt/lagos/field_info_container.py", line 297, in get_dependencies self(e) File "/projects/lca-group/local-dev/lib/python2.6/site-packages/yt-2.0dev-py2.6-linux-x86_64.egg/yt/lagos/field_info_container.py", line 318, in __call__ dd = self._function(self, data) File "xtra_fields.py", line 161, in _TE dataset = data.hierarchy.io.pop(data, 'TotalEnergy') AttributeError: 'fake_io' object has no attribute 'pop' -- Sent from my Stone Tablet and carried by my Pterodactyl.