A feedback device (400; 600; 650) for an aircraft-bladed rotor rotating about a longitudinal axis (A), the feedback device (400; 600; 650) comprising: a circular disk having first and second opposing faces and defining a root surface that extends between and circumscribes the first and second faces , the circular disk comprising a first material having a first magnetic permeability; and a plurality of position markers extending radially from the root surface and circumferentially spaced around the circular disk , the position markers having a top surface elevated with respect to the root surface and opposing first and second side surfaces joining the root surface to the top surface , characterised in that : the first and second side surfaces of the position markers include a straight first portion extending from the top surface towards the root surface and connecting to a second portion which joins with the root surface , the second portion having a curved concave profile extending toward the root surface ; and some or all of the position markers comprise a top portion comprising a second material having a second magnetic permeability higher than the first magnetic permeability, the top portion including the top surface and extending therefrom toward the root surface by a predetermined distance. device (400; 600; 650) comprising: a circular disk having first and second opposing faces and defining a root surface that extends between and circumscribes the first and second faces , the circular disk comprising a first material having a first magnetic permeability; and a plurality of position markers extending radially from the root surface and circumferentially spaced around the circular disk , the position markers having a top surface elevated with respect to the root surface and opposing first and second side surfaces joining the root surface to the top surface , a circular disk having first and second opposing faces and defining a root surface that extends between and circumscribes the first and second faces , the circular disk comprising a first material having a first magnetic permeability; and a plurality of position markers extending radially from the root surface and circumferentially spaced around the circular disk , the position markers having a top surface elevated with respect to the root surface and opposing first and second side surfaces joining the root surface to the top surface , characterised in that : the first and second side surfaces of the position markers include a straight first portion extending from the top surface towards the root surface and connecting to a second portion which joins with the root surface , the second portion having a curved concave profile extending toward the root surface ; and some or all of the position markers comprise a top portion comprising a second material having a second magnetic permeability higher than the first magnetic permeability, the top portion including the top surface and extending therefrom toward the root surface by a predetermined distance. the first and second side surfaces of the position markers include a straight first portion extending from the top surface towards the root surface and connecting to a second portion which joins with the root surface , the second portion having a curved concave profile extending toward the root surface ; and some or all of the position markers comprise a top portion comprising a second material having a second magnetic permeability higher than the first magnetic permeability, the top portion including the top surface and extending therefrom toward the root surface by a predetermined distance. <EOS>