Del Grosso's equation
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An alternative equation to the UNESCO algorithm, which has a more restricted range of validity, but which is preferred by some authors, is the Del Grosso equation (1974). Wong and Zhu (1995) also reformulated this equation for the new 1990 International Temperature Scale and their version is:
c(S,T,P) = ^{ }  C_{000} + C_{T} + C_{S} + C_{P} + C_{STP} ^{ } 
C_{T}(T) = C_{T1}T + C_{T2}T^{2} + C_{T3}T^{3}  
C_{S}(S) = C_{S1}S + C_{S2}S^{2}  
C_{P}(P) = C_{P1}P + C_{P2}P^{2} + C_{P3}P^{3}  
C_{STP}(S,T,P) = C_{ST}ST + C_{TP}TP + C_{TP2}TP^{2} + C_{T3P}T^{3}P + C_{T2P2}T^{2}P^{2} + C_{TP3}TP^{3} + C_{ST2}ST^{2} + C_{STP}STP + C_{S2TP}S^{2}TP + C_{S2P2}S^{2}P^{2}  
T = temperature in degrees Celsius S = salinity in Practical Salinity Units P = pressure in kg/cm^{2} 
Range of validity: temperature 0 to 30 C, salinity 30 to 40 parts per thousand, pressure 0 to 1000 kg/cm^{2}, where 100 kPa=1.019716 kg/cm^{2}. (Wong and Zhu, 1995).
Please note that for consistency, within the interactive version, the pressure must be input in kPa.

(2)G.S.K. Wong and S Zhu, Speed of sound in seawater as a function of salinity, temperature and pressure (1995) J. Acoust. Soc. Am. 97(3) pp 17321736