The constants a 1, a 2,..., a 9 are a 1 = 1 , 448.96 , a 2 = 4.591 , a 3 = − − 5.304 × × 10 − − 2 , a 4 = 2.374 × × 10 − − 4 , a 5 = 1.340 , a 6 = 1.630 × × 10 − − 2 , a 7 = 1.675 × × 10 − − 7 , a 8 = − − 1.025 × × 10 − − 2 , a 9 = − − 7.139 × × 10 − − 13 , with check value 1 550.744 m/s for T = 25 °C, S = 35 parts per thousand, z = 1,000 m. This equation has a standard error of 0.070 m/s for salinity between 25 and 40 ppt. See [1] for an online calculator.