de>[[</code> method can also be used to get
certain derived quantities, if the object contains sufficient
information to calculate them. For example, an object that holds
(practical) salinity, temperature and pressure, along with
longitude and latitude, has sufficient information to compute
Absolute Salinity, and so <code>o[["SA"]]</code> will yield the
calculated Absolute Salinity.</p>
<p>It is also possible to find items more directly, using <code><a href="oceGetData.html">oceGetData()</a></code> and
<cod