We use them for our business. They are ok for a quick reading, but not very accurate at multiple scales. Our probes scale is 0 -10,000 ppm. Example, if TDS is between 4,000 and 5,000 ppm our meter is fairly accurate. If I want a reading between 8,000 - 9,000 ppm, forget about it. Same goes for 0 - 250 ppm, not very acccurate. They have more accurate probes that read uS, but are very expensive, or an older Myron L Company analog type meter.