Unit for measuring the settling velocity of particles in suspension in a fluid from a source, the unit comprising: - a sealed container having an opening, the container defining an open compartment that comprises the opening and a sealed compartment, sealing means separating the open compartment from the sealed compartment, the open compartment being intended to contain a sample of the fluid to be analysed; - means for measuring the settling velocity of the particles of the sample in the open compartment, said measuring means being placed in the sealed compartment of the container, said measuring means being of the optical type and comprising: • at least three emitters of electromagnetic radiation, the emitters being distributed along a longitudinal axis of the open compartment, each emitter being oriented along a radiation axis crossing the open compartment at different heights along the longitudinal axis on the open compartment; • receivers, the number of which is equal to the number of emitters and which are distributed along the longitudinal axis, each receiver being placed in the radiation axis of an emitter, so as to receive the radiation from the corresponding emitter after passing through the open compartment; • means for controlling the emitters and the receivers; • a system for acquiring data connected to the receivers for collecting the data of the measurements carried out, the data acquired making it possible to obtain the settling velocity of the particles and its variation as a function of the height in the open compartment and as a function of time, said variation quantifying a flocculation of the particles. - a sealed container having an opening, the container defining an open compartment that comprises the opening and a sealed compartment, sealing means separating the open compartment from the sealed compartment, the open compartment being intended to contain a sample of the fluid to be analysed; - means for measuring the settling velocity of the particles of the sample in the open compartment, said measuring means being placed in the sealed compartment of the container, said measuring means being of the optical type and comprising: • at least three emitters of electromagnetic radiation, the emitters being distributed along a longitudinal axis of the open compartment, each emitter being oriented along a radiation axis crossing the open compartment at different heights along the longitudinal axis on the open compartment; • receivers, the number of which is equal to the number of emitters and which are distributed along the longitudinal axis, each receiver being placed in the radiation axis of an emitter, so as to receive the radiation from the corresponding emitter after passing through the open compartment; • means for controlling the emitters and the receivers; • a system for acquiring data connected to the receivers for collecting the data of the measurements carried out, • at least three emitters of electromagnetic radiation, the emitters being distributed along a longitudinal axis of the open compartment, each emitter being oriented along a radiation axis crossing the open compartment at different heights along the longitudinal axis on the open compartment; • receivers, the number of which is equal to the number of emitters and which are distributed along the longitudinal axis, each receiver being placed in the radiation axis of an emitter, so as to receive the radiation from the corresponding emitter after passing through the open compartment; • means for controlling the emitters and the receivers; • a system for acquiring data connected to the receivers for collecting the data of the measurements carried out,