function rt = sw_salrt(T)

% SW_SALRT   Conductivity ratio   rt(T)     = C(35,T,0)/C(35,15,0)
%=========================================================================
% SW_SALRT  $Id$
%           Copyright (C) CSIRO, Phil Morgan 1993.
%
% USAGE:  rt = sw_salrt(T)
%
% DESCRIPTION:
%    Equation rt(T) = C(35,T,0)/C(35,15(IPTS-68),0) used in calculating
%       salinity.
%    UNESCO 1983 polynomial.
%
% INPUT:
%   T = temperature [degree C (ITS-90)]
%
% OUTPUT:
%   rt = conductivity ratio  [no units]
%
% AUTHOR:  Phil Morgan 93-04-17, Lindsay Pender (Lindsay.Pender@csiro.au)
%
% DISCLAIMER:
%   This software is provided "as is" without warranty of any kind.
%   See the file sw_copy.m for conditions of use and licence.
%
% REFERENCES:
%    Fofonoff, P. and Millard, R.C. Jr
%    Unesco 1983. Algorithms for computation of fundamental properties of
%    seawater, 1983. _Unesco Tech. Pap. in Mar. Sci._, No. 44, 53 pp.
%

% Modifications
% 03-12-12. Lindsay Pender, Converted to ITS-90.

% CALLER: sw_salt
% CALLEE: none

% rt = rt(T) = C(35,T,0)/C(35,15,0)
% Eqn (3) p.7 Unesco.

T68 = T * 1.00024;

c0 =  0.6766097;
c1 =  2.00564e-2;
c2 =  1.104259e-4;
c3 = -6.9698e-7;
c4 =  1.0031e-9;

rt = c0 + (c1 + (c2 + (c3 + c4.*T68).*T68).*T68).*T68;

return
