Auto LCD Digital Pen Shape PH MeterHold Function saves measurements for convenient reading and recording.//Auto-off function : the meter shuts off automatically after 10 minutes of non-use to conserve batteries.//Measurement Range : 0-9990 ppm. From 0-999 ppm, the resolution is in increments of 1ppm. From 1000 to 9990 ppm, the resolution is in increments of 10ppm, indicated by a blinking ‘x10′ image.//Display : large and easy-to-read LCD screen.Factory Calibrated : our meters are calibrated with a 342 ppm NaCl solution. Includes a TDS chart sticker on the back of the meter that explains TDS values.