A feedback device (400; 600; 650) for an aircraft-bladed rotor rotating about a longitudinal axis, the feedback device (400; 600; 650) comprising: a circular disk having first and second opposing faces (416, 418) and defining a root surface that extends between and circumscribes the first and second faces (416, 418), 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 (406, 408) joining the root surface to the top surface, characterised in that: the first and second side surfaces (406, 408) 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 (416, 418) and defining a root surface that extends between and circumscribes the first and second faces (416, 418), 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 (406, 408) joining the root surface to the top surface, a circular disk having first and second opposing faces (416, 418) and defining a root surface that extends between and circumscribes the first and second faces (416, 418), 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 (406, 408) joining the root surface to the top surface, characterised in that: the first and second side surfaces (406, 408) 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 (406, 408) 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.