A source of a gaseous substance, an inner subassembly and an outer subassembly having an outer enclosure comprising, a counter (20) accommodated within the outer enclosure (11) for counting substance release displacements of the spout (4); and a counter actuation member arranged beside the spout (4) for displacement inwards to increment the counter (20), the outer subassembly having an overall length from the actuation member at the spout (4) to a pressurised-container reaction surface, which length decreases on substance release and having at least a first quiescent length and a second length at which counter incrementation is initiated, €¢ the subassembly also having a tolerance adjusted connection of the cap (105) to the outer enclosure (11) set with respect to a use installation of the source, whereby the stroke between the first and second lengths of the respective subassemblies is compensated for synchronisation of substance release and count incrementation.