This method required the introduction of a very small volume of concentrated tracer at the inlet of the reactor, such that it approaches the Dirac delta function. Although an infinitely short injection cannot be produced, it can be made much smaller than the mean residence time of the vessel. If a mass of tracer, , is introduced into a vessel of volume  and an expected residence 
time of , the resulting curve of  can be transformed into a dimensionless residence time distribution curve by the following relation: