Refractometer-Ad Blue-Sealey-VS0051-Refractometer-designed-to-measure-aqueous-urea-content-of-Ad Blue-additive-Ensures-Ad Blue-additive-is-correctly-diluted-before-adding-to-vehicle-s-Ad Blue-tank-Measures-refractive-index-of-fluid-using-only-a-drop-of-Ad Blue-Simple-calibration-check-using-distilled-water-Fitted-with-adjustable-eyepiece-&-supplied-in-storage-case-Refractometer-Ad Blue