Minor grammar edits to docs

docs/conventions.md

@@ -2,7 +2,7 @@
 
 ## Units
 
-We use SI units for the model parameters, except for angles (we use degrees instead of radians) and target strength (we use deciBels).  All model code must accept inputs and produce results using the units below. If the model calculations use different units internally, the code should internally convert between them.
+We use SI units for the model parameters, except for angles (degrees instead of radians) and target strength (deciBels).  All model code must accept inputs and produce results using the units below. If the model calculations use different units internally, the code should internally convert between them.
 
 | Parameter | Units | Notes |
 |-----------|-------|--|

docs/usage.md

@@ -8,7 +8,7 @@ EchoSMs is available on [PyPi](https://pypi.org) as [`echosms`](https://pypi.org
 
     pip install echosms
 
-The prolate spheroidal modal series model in echoSMs uses spheroidal wave functions. A high-accuracy implementation of these is available in the Python package [`spheroidalwavefunctions`](https://pypi.org/project/spheroidalwavefunctions/), as the versions provided by [scipy](https://docs.scipy.org/doc/scipy/reference/special.html#spheroidal-wave-functions) are insufficient. This should be installed automatically when you install echosms, but note that `spheroidalwavefunctions` is currently only available for Linux and Windows on x86_64 CPU architectures (create an [issue](https://github.com/ices-tools-dev/echoSMs/issues) if you want it on a system that is not currently supported).
+The prolate spheroidal modal series model in echoSMs uses spheroidal wave functions. A high-accuracy implementation of these is available in the [`spheroidalwavefunctions`](https://pypi.org/project/spheroidalwavefunctions/) Python package , as the functions provided by [scipy](https://docs.scipy.org/doc/scipy/reference/special.html#spheroidal-wave-functions) are insufficient. This should be installed automatically when you install echosms, but note that `spheroidalwavefunctions` is currently only available for Linux and Windows on x86_64 CPU architectures (create an [issue](https://github.com/ices-tools-dev/echoSMs/issues) if you want it on a system that is not currently supported).
 
 ## Versions
 
@@ -117,7 +117,7 @@ When passing a DataFrame to a model, you can choose whether the TS results are r
 
 Some models use parameters that are not sensibly duplicated across rows in a DataFrame or as a dimension in a DataArray (e.g., the data that specifies the three-dimensional shape of a fish swimbladder). EchoSMs allows for this with the concept of _non-expandable_ parameters - these are not expanded into DataFrame columns or DataArray dimensions. Non-expandable parameter names are available from the models' `no_expand_parameters` attribute.
 
-But, as it is very convenient to have all the model parameters in one data structure, echoSMs will store the non-expandable parameters as DataFrame or DataArray attributes. Due to a bug in the DataFrame implementation, the parameters are stored as a nested dictionary under a `parameters` attribute. An example of this is the `PTDWBAModel`:
+But, as it is very convenient to have all the model parameters in one data structure, echoSMs will store the non-expandable parameters as a dict in the DataFrame or DataArray attributes. An example of this is the `PTDWBAModel`:
 
 ```py
     from echosms import PTDWBAModel, as_dataframe
@@ -278,7 +278,7 @@ Note that the `parameters()` call does not return all of the parameters needed b
     bm.freq_dataset  # the TS as a function of frequency
 ```
 
-The TS and frequency values for a particular benchmark are available with normal Pandas DataFrame indexing syntax. The DataFrame columns names are the same as the ReferenceModels names. For example:
+The TS and frequency values for a particular benchmark are available with normal Pandas DataFrame indexing syntax. The DataFrame column names are the same as the ReferenceModels names. For example:
 
 ```py
     bm.freq_dataset['weakly scattering sphere']