Valid point which I glossed over aleman
I'm happy enough with a little variation. I can guesstimate where the levels will be. For most beers I'm ok just adding a touch more chloride or sulphate without being anal about values.
Anyway. If noone else finds it useful, I sure do. Just checked it with my strike and sparge water (brewing currently) and both times its been spot on (+-4ppm). Happy days