Improve get_data_in_units docstring (#1880)

* Improve get_data_in_units docstring

* Update base.py

---------

Co-authored-by: Cody Baker <51133164+CodyCBakerPhD@users.noreply.github.com>

src/pynwb/base.py

@@ -343,14 +343,17 @@ def get_data_in_units(self):
         .. math::
             out = data * conversion + offset
 
-        If the field 'channel_conversion' is present, the conversion factor is applied to each channel separately:
+        If the field 'channel_conversion' is present, the conversion factor for each channel is additionally applied 
+        to each channel:
 
         .. math::
-            out_{channel} = data * conversion_{channel} + offset
+            out_{channel} = data * conversion * conversion_{channel} + offset
+
+        NOTE: This will read the entire dataset into memory.
 
         Returns
         -------
-        np.ndarray
+        :class:`numpy.ndarray`
 
         """
         if "channel_conversion" in self.fields: