How to Calibrate the ORP Meter:1. ON/OFF button to turn on the meter, the protective cap and rinse off the probe with pure water and dry it. 2. the "MODE/CAL" button to set the ORP mode; the word "mV" be displayed at the top right of the screen. Put the probe into 222mV calibration solution and shake it gently. 3. Wait until the reading is stable, then long "MODE/CAL" for 5 seconds and release; CAL is displayed on the screen, then a value flash 3 times on the screen, when the value starts to fiash, "MODE/CAL" button ( lf the flashing value is higher than 222mV ) or "HOLD/TEMP" button ( lf the flashing value is lower than 222mV ). 4. After adjusting the displaying value to 222mV then release the button, waiting the reading stop flashing,the calibration is finished, rinse off the probe with water. Storage: Buffer solutions should be stored in a dark, cool place (not in the refrigerator and at temperatures no higher than 25C) away from direct sunlight to prevent photochemical degradation. In addition, buffer calibration solutions should be protected from carbon dioxide from the air and stored in tightly closed containers. Colour:As Shown Material:plastic type:ORP 222mV Package Contents: 1 set x pH Meter Only the above package content, other products are not included. Note: Light reflection and different displays may cause the color of the item in the picture a little different from the real thing. The measurement allowed error is +/- 1-3cm.