Tier1 Digital Water Quality Test Meter for Total Dissolved Solids (TDS) Dual range measurement: 0-999 ppm with resolution 1ppm, 1000-9990 ppm with resolution 10ppm Measurement accuracy of +/- 2 Percent 10 minute auto-shutoff to conserve battery life Hold function saves measurements for convenient reading and recording Test water periodically to ensure water filter is doing its job