Review on ⚖️ Accurate TDS Meter Digital Water Tester: Third Wave Water 0-9999ppm for Optimal Coffee Brewing Water Composition by Chris Lemm

I bought a couple of these TDS meters, both are about the same price and seem to be the same quality. After we tried both in fresh McMaster/Carr deionized (deionized) water, they both showed zero. After trying them both in dirty deionized water currently in an EDM drill, another said 7 and this one said 14. After trying them in a cup of tap water, another said 110 and this one said 230. Although their readings are quite different, I think any of these gauges will work to measure the degradation of the deionized water in our EDM machine once I see what the numbers are before drilling issues become noticeable. Also, unfortunately, I have no way of determining which is closer to absolute accuracy.