Hanna Instruments offer the most advanced pens on the market today. The pHep4 pH/Temperature Waterproof Pen has a .01 ph resolution. The Dist5 EC/TDS Pen is unmatched in EC/TDS/Temperature measurement. The Combo pH/EC/TDS/Temperature Pen offers highly advanced accuracy with a single tester. All Hanna Instruments pens offer replaceable graphite electrode, temperature in °C or °F, automatic temperature compensation with adjustable battery level indicator, stability indicator, automatic shut-off and automatic calibration all in a floating waterproof casing.