Abstract: A measuring device for a liquid meter with oscillating piston comprises a hollow chamber pierced with two apertures and limited by a cylindrical side wall, a bottom and a lid; a piston enclosed in said chamber and held movably, along a partition wall about a well. This device further comprises at least one groove, made in the corners formed between the bottom and the side wall of the chamber or the well or the piston, that opens into the hollow of the chamber, in a space formed between the well and the side walls, and is designed to receive deposits of particles introduced into said device by the liquid to be metered. The device can be applied in particular to water metering. FIG.