Step 1: Open the cover plate, add 2-3 drops of distilled water or standard solution onto the surface of the prism, close the cover plate, and let the sample solution cover the entire surface of the prism without leaving any bubbles or gaps. Before proceeding with the first step, leave the sample solution on the cover plate for about 30 seconds, which can ensure that the temperature around the sample and refractometer is consistent.

Step 2: Place the refractometer under the light source and observe through the eyepiece. You will see a circular area marked with a scale. If the image is not clear enough, you can adjust the focusing cylinder to make the scale line clearer. The upper part of the area is blue, and the lower part is white.

Step 3: Use distilled water or standard solution as the sample, observe through the eyepiece, and adjust the calibration screw until the boundary between the blue and white fields completely coincides with the 0 scale line. At this point, the calibration is complete. Try to ensure that the surrounding temperature is within the range of 20 degree C or 68 degree F, which will not affect the accuracy of the measurement. When the temperature fluctuation in the working environment exceeds 5 degrees, please recalibrate to ensure the accuracy and reliability of the measurement results. If the refractometer is equipped with an automatic temperature compensation system, regardless of when the instrument is recalibrated, it must be ensured that the ambient temperature during calibration is 20 degree or 68 ℉. Once calibrated, the temperature of the surrounding environment can fluctuate within the allowable range (10 degree ~30 degree ) without affecting the accuracy of the measurement.

Step 4: Use the sample solution of the solution to be measured instead of distilled water or calibration solution, then repeat the first step, followed by the second and third steps. Read the scale value of the blue white boundary, and the current scale value is the accurate measurement value of the concentration of the sample solution.