SX610 Waterproof pH Pen Tester, &plusmn;0.1 pH Accuracy, 0-14.0 pH Range, Suitable for Test Tube Testing, Replaceable Probe Easy SINGLE-Button Operation, Smallest Pen-Style design with replaceable probe (good for test tube measurements) AUTO Calibration with auto buffer recognition; Auto Temperature Compensation (ATC) ensures accuracy in variant temperatures (0-60.0C) COMPLETE KIT with READY-TO-USE calibration solution, KCl storage solution, and batteries in a portable carrying case Intelligent functions: temperature unit switch from F to C, automatic power-off, low battery alarm, and pH probe invalidation reminder AUTO RECOGNITION and REMINDER of stable values improves consistency, saving you the trouble of guessing when to manually hold measurement