System for measuring the axial movement of a mobile part rotating on an axis A, comprising: - a magnetic coding device, comprising at least one annular track on which are magnetized a plurality of north and south pole pairs (3, 4), equidistant, exhibiting a helical form of axis A; - a magnetic field detection device comprising at least one first and one second fixed magnetic sensor, arranged at a non-zero axial distance d from one another, radially opposite and at a reading distance from the annular track of the coding device and sensitive to the variations of the magnetic field induced by the coding device, the second sensor delivering a pseudo-sinusoidal signal REF; characterized in that - the first sensor comprises: - a first plurality of aligned sensitive elements, the sensitive elements being divided into at least two first subsets; and - an electronic circuit arranged to deliver two analogue signals SIN1 and COS1 of the same amplitude in quadrature as a function of the signals from the first subsets and - the measurement system comprises: - a first spatial resolution multiplier for generating, from the two analogue signals SIN1 and COS1 in quadrature, at least one first digital signal changing state N1 times per magnetic period, N1 being an integer number greater than or equal to 4; - a computer for determining the instantaneous angular phase-shift between the magnetic field seen by the first sensor and the magnetic field seen by the second sensor, as a function of the first digital signal, of the signal SIN1 and of the signal REF. - a magnetic coding device, comprising at least one annular track on which are magnetized a plurality of north and south pole pairs (3, 4), equidistant, exhibiting a helical form of axis A; - a magnetic field detection device comprising at least one first and one second fixed magnetic sensor, arranged at a non-zero axial distance d from one another, radially opposite and at a reading distance from the annular track of the coding device and sensitive to the variations of the magnetic field induced by the coding device, the second sensor delivering a pseudo-sinusoidal signal REF; - the first sensor comprises: - a first plurality of aligned sensitive elements, the sensitive elements being divided into at least two first subsets; and - an electronic circuit arranged to deliver two analogue signals SIN1 and COS1 of the same amplitude in quadrature as a function of the signals from the first subsets and - a first plurality of aligned sensitive elements, the sensitive elements being divided into at least two first subsets; and - an electronic circuit arranged to deliver two analogue signals SIN1 and COS1 of the same amplitude in quadrature as a function of the signals from the first subsets and - the measurement system comprises: - a first spatial resolution multiplier for generating, from the two analogue signals SIN1 and COS1 in quadrature, at least one first digital signal changing state N1 times per magnetic period, N1 being an integer number greater than or equal to 4; - a computer for determining the instantaneous angular phase-shift between the magnetic field seen by the first sensor and the magnetic field seen by the second sensor, as a function of the first digital signal, of the signal SIN1 and of the signal REF. - a first spatial resolution multiplier for generating, from the two analogue signals SIN1 and COS1 in quadrature, at least one first digital signal changing state N1 times per magnetic period, N1 being an integer number greater than or equal to 4; - a computer for determining the instantaneous angular phase-shift between the magnetic field seen by the first sensor and the magnetic field seen by the second sensor, as a function of the first digital signal, of the signal SIN1 and of the signal REF.