Holy crap, ammonium nitrate has even MORE N in it than ammonium sulfate! In fact, isn't that the shit from seabird guano that used to be mined for the explosives industry? That N=N bond is good for blowing things up!

The meter I speak of...

I'm a chemist. I'm at work (yes, it's a holiday, I DON'T want to be here!). I have a rather high-end pH meter at my disposal.

For home use, I cheaped out and went with a lifetime supply of pH indicator that General Hydroponics makes. It was $12.

Wait- I'm rereading your post- the digital scale- that's the one for weighing ounces. It's accurate enough for weighing grams of dry fertilizer.