Abstract: The invention provides a method for determining the degree of partial occlusion of a conduit, comprising the steps of:a) producing a graphical plot of fluid pressure versus fluid flow rate through said conduit;b) determining the value of one or more of the following variables:(iv) the PFLA variable consisting of the area enclosed by said graphical plot;(v) the slope of the line joining the two inflection points situated at the extremities of the major axis of said graphical plot;(vi) the y-axis intercept of the line joining the two inflection points situated at the extremities of the major axis of said graphical plot;c) determining the degree of partial occlusion of said conduit by comparing one or more of the above variables, with an appropriate calibration curve, said calibration curve comprising values of the chosen variable for a conduit of the same type as the tested conduit, at predetermined known degrees of occlusion.