I used to check chemical levels in boiler, cooling tower, and chilled water loops. Used a PPM meter that had a ceramic bowl mounted a four inch square base with a simple push button on the front. I am sure back then they were an analog device, and they were built like a little tank. I would like to have one of those now. I have seen some cheap imitations of it online, and I am sure these use the same modern technology as the cheaper pens.
That is very similar, and the same company I believe. I always found the water treatment side of working on chillers very interesting.
Good information guys. Love it.