user _graph help!

[tianshiyu]

I now use phreeqc to simulate the change of free ammonia in ammonia buffer solution with pH. I tried to draw the relationship between AmmH+ and pH with GRAPH_X -la("H+")/GRAPH_Y tot("AmmH+")*15, but it didn't work. What should I do?
Thank you very much for your help!

[dlparkhurst]

Basic functions are described in the manual. TOT("Amm") will give the total amount of Amm, including all aqueous species, in mol/kgw.