Does it measure the concentration of 2-stroke oil in the mixture?

When fuel from your engine is added to the reactant, the mixture will remain clear if no oil is present. The mixture will turn opaque if oil is present in sufficient quantity. Familiarity with results will enable the user to determine the ratio of oil/petrol. It is recommended that new users test a known sample to use as a reference. This only need be done once for although the sample will gradually clear, all that is needed is to agitate the vial to restore the effect.