How do I calculate seawater properties?

Q: How do I calculate seawater properties?

SEAWATER Library is available at http://www.marine.csiro.au/~morgan/seawater/.
Another one (OCEANS toolbox ) is at ftp://acoustics.whoi.edu/pub/Matlab/oceans/ ("A collection of routines useful for oceanographers, including the UNESCO routines (specific heat capacity, the equation of state, etc.), various sound-speed equations, T/S diagrams, distances on an ellipsoidal earth, and more.")

Here is the list of functions from the former:

% SEAWATER Library Version 1.2e
%
%                  ******************************* 
%                  *      SEAWATER Library       * 
%                  *                             * 
%                  *       Version 1.2e          * 
%                  *                             * 
%                  *     Phillip P. Morgan       * 
%                  *           CSIRO             * 
%                  *                             *
%                  * Phil.Morgan@marine.csiro.au *
%                  ******************************* 
%
% LIST OF ROUTINES:
%
%     SW_NEW     What's new in this version of seawater.
%
%     SW_ADTG    Adiabatic temperature gradient 
%     SW_ALPHA   Thermal expansion coefficient (alpha) 
%     SW_AONB    Calculate alpha/beta (a on b) 
%     SW_BETA    Saline contraction coefficient (beta) 
%     SW_BFRQ    Brunt-Vaisala Frequency Squared (N^2)
%     SW_COPY    Copyright and Licence file
%     SW_CP      Heat Capacity (Cp) of Sea Water 
%     SW_DENS    Density of sea water 
%     SW_DENS0   Denisty of sea water at atmospheric pressure 
%     SW_DIST    Distance between two lat, lon coordinates
%     SW_DPTH    Depth from pressure 
%     SW_F       Coriolis factor "f" 
%     SW_FP      Freezing Point of sea water 
%     SW_G       Gravitational acceleration 
%     SW_GPAN    Geopotential anomaly  
%     SW_GVEL    Geostrophic velocity 
%     SW_INFO    Information on the SEAWATER library. 
%     SW_PDEN    Potential Density 
%     SW_PRES    Pressure from depth 
%     SW_PTMP    Potential temperature 
%     SW_SALS    Salinity of sea water 
%     SW_SALT    Salinity from cndr, T, P 
%     SW_SVAN    Specific volume anomaly 
%     SW_SVEL    Sound velocity of sea water 
%     SW_SMOW    Denisty of standard mean ocean water (pure water) 
%     SW_TEMP    Temperature from potential temperature 
%     SW_TEST    Run test suite on library
%     SW_VER     Version number of SEAWATER library
%
% LOW LEVEL ROUTINES CALLED BY ABOVE: (also available for you to use)
%
%     SW_C3515   Conductivity at (35,15,0) 
%     SW_CNDR    Conductivity ratio   R = C(S,T,P)/C(35,15,0) 
%     SW_SALDS   Differiential dS/d(sqrt(Rt)) at constant T. 
%     SW_SALRP   Conductivity ratio   Rp(S,T,P) = C(S,T,P)/C(S,T,0) 
%     SW_SALRT   Conductivity ratio   rt(T)     = C(35,T,0)/C(35,15,0) 
%     SW_SECK    Secant bulk modulus (K) of sea water 
%=======================================================================