681.5 g/kg = 684.839 PSU
| g/kg | PSU |
|---|---|
| 666.5 g/kg | 669.766 |
| 671.5 g/kg | 674.79 |
| 676.5 g/kg | 679.815 |
| 681.5 | 684.839 |
| 686.5 g/kg | 689.864 |
| 691.5 g/kg | 694.888 |
| 696.5 g/kg | 699.913 |
681.5 g/kg = 684.839 PSU
1 g/kg ≈ 1.0049 PSU · 1 mg/L ≈ 0.001 PSU · 1 ppm ≈ 0.001 PSU (dilute aqueous approximation)