This document specifies a method for the determination of the thickness of the lacquer film applied inside cylindrical and conical aluminium tubes. The method is a reference. It can also be used as a reference when calibrating other electronic instruments suitable for determining coating weight thickness, e.g. by capacitance measurement by eddy current. It is applicable to aluminium tubes used for packing pharmaceutical, cosmetic, hygiene, food and other domestic products. NOTE Although not specified in this standard there are available suitable automatic film thickness measurement instruments that provide instantaneous results with good accuracy (< 1µm).