the pressure differences between subsequent samples. If
these are all of the same value, then the input <code>ctd</code> object is returned, unaltered.
This handles the case of pressure-binned data. However, if the pressure difference
varies, a variety of approaches are taken to trimming the dataset.</p><ul><li><p>If <code>method[1]</code> is <code>"downcast"</code> then an attempt is made to keep only data for
which the CTD is descending.  This is done in stages, with variants based on <code>method[2]</cod