You asked me to give you the reference and I did. But here we go...

You asked me to give you the reference and I did. But here we go anyway. The table that Reward have in their 12 November 2015 announcement at Appendix 2 on page 6 lists various cation grades. For example, it lists Ca, K, MG and Na, and then also SO4 and Cl.
It then purports to calculate an SOP grade from the K grade, which if you were GPH, AMN or even SO4, would simply be K x 2.23.
So lets pick a random sample of 5 K grades from the RWD announcement:
1. K = 2.16
per RWD this equates to an SOP grade of 13.69, per GPH/AMN this would be 4.81
2. K = 4.30
per RWD this equates to an SOP grade of 15.36, per GPH/AMN this would be 9.58
3. K = 2.04
per RWD this equates to an SOP grade of 11.74, per GPH/AMN this would be 4.54
4. K = 3.81
per RWD this equates to an SOP grade of 12.99, per GPH/AMN this would be 8.49
5. K = 3.73
per RWD this equates to an SOP grade of 15.77, per GPH/AMN this would be 8.31
Comprende'