Review on 📈 APERA INSTRUMENTS AI209 Value Series PH20 Waterproof pH Tester Kit - Accurate to ±0.1 pH by Chuck Hernandez

It took a little practice and experimentation to learn how to calibrate this measuring pin. A long press on the CAL button puts the instrument into calibration mode and a short press on the MEAS button aborts the calibration process. The instructions combine these two steps into the same step, which confuses me. To calibrate, press and hold the CAL button, then place the probe in the 7.00 buffer until the smiley appears on the display. Take your time, let the device stabilize and then press the CAL button shortly. If the display shows the letter "M", it means that you have correctly performed the 1-point calibration. Rinse the probe in distilled water (referred to as "clean water” in the instructions) and dry the probe. (Be careful not to scratch or damage the electrode bulb! Gently blot the bulb with an absorbent pad or paper towel.) Press and hold the CAL button again to begin the second point calibration. Insert the probe into Buffer 4.00 and wait for the smiley. Briefly press the CAL button and observe the letter "L” on the display. You have completed the 2nd point calibration. Rinse the sensor in distilled water, dry the sensor and you are now ready to measure the pH of your solution.