✔ SPECIFICALLY DESIGNED REFRACTOMETER FOR SALTWATER AQUARIUM--The algorithm is made specifically for testing seawater and saltwater. This is different than a standard refractometer which is not calibrated to check salinity of aquarium water and will give an error in your readings. ✔ AUTOMATIC TEMPERATURE CALIBRATION --- The calibration process should be carried out with both the room and the instrument at 68° F. The refractive index of a liquid changes with temperature. Due to the automatic temperature calibration, any changes in ambient temperature from 50° F- 86° F will not affect the accuracy of the reading. ✔ EASY AND CLEAR READING FOR SALTWATER AQUARIUMS AND REEF TANKS--- The refractometer comes with a focus adjustment on the eyepiece, this will give you clarity of the optics and a sharp line for easy reading. ✔ COMES IN A SOLID CASE INCLUDES PIPETTE AND CALIBRATION TOOL --- This 7.6 inches refractometer is not only built extremely well, but it comes with a durable hard case for safe and easy storage of the refractometer when not in use. It also includes a calibration tool and a pipette. ✔ KEEP YOUR FISH AND PLANT LIFE IN OPTIMAL HEALTH--- Clean, pure saltwater is crucial for the vitality of your marine or reef aquarium. Use this refractometer to measure the salinity of the water, the target level of salinity in a reef tank should be 35 ppt.