Abstract: This invention relates to a device for indicating the temporally variable quantity of a liquid contained in a reservoir or tank, whatever the indication of this reservoir with respect to the horizontal, wherein the device comprises an auxiliary recipient fast with the reservoir, which is arranged therewith in an at least partially enveloping arrangement and which contains an invariable quantity of an auxiliary liquid of which the level serves as reference for assessing, by comparison of level, the variable quantity of liquid contained at a given instant in the reservoir. The invention is more particularly applicable to the determination of the level of fuel in a tank connected to a vehicle, of the oil in a gearbox of a vehicle, etc.