The Primo pocket TDS meter gives a direct digital readout in mg/L (1mg/L is the same as 1ppm), on a clear LCD display and is ideal for water testing. The meter has a single button located on the top of the meter, which is pressed once to switch on and ready for use. Battery life is an impressive 200 hours, which is further enhanced by the automatic switch-off after 5 minutes of inactivity. To calibrate the meter, simply press and hold the button for a few seconds and the Primo will automatically enter calibration mode. Simply place the Primo sensor in the calibration solution and within seconds the meter will automatically recognise the value of the solution and self-calibrate - no further pressing of buttons required. Primo uses calibration solution with a value of 1382ppm/mg per L which is Hanna part number HI-70032P. For the full product specification please see the attached instruction manual. The Primo is supplied complete with batteries and instructions.