A sheet edge detection device for a printing system, comprising: - a transport path for transporting a sheet to an image forming unit of the printing system, which transport path comprises a calibration transport path section and arranged for transporting sensed sheets to the image forming unit during a calibration of the sheet edge detection device; - a detector assembly comprising at least one detector unit positioned upstream of the calibration transport path section, which at least one detector unit comprises an emitter and a detector positioned on opposite sides of the transport path, wherein the at least one detector unit is arranged to generate signal data defining a signal data curve as a sheet passes the at least one detector unit; - a processor configured for: - receiving signal data from the detector assembly; - calibrating a signal threshold by: - deriving a first signal level from the signal data corresponding to a state wherein no sheet is present between one of the at least one detector unit; - deriving a second signal level from the signal data corresponding to a state wherein a sheet covers the detector of the at least one detector unit, as seen in an emission direction from the emitter to the detector; - selecting the signal threshold to lie in between the first signal level and the second signal level; - comparing a signal data curve received from the detector assembly to the determined signal threshold to determine an intersection between said signal data curve and said signal threshold; - determining a position of a point on a sheet edge of the sheet as said sheet moves over the calibration transport section from the intersection. - a transport path for transporting a sheet to an image forming unit of the printing system, which transport path comprises a calibration transport path section and arranged for transporting sensed sheets to the image forming unit during a calibration of the sheet edge detection device; - a detector assembly comprising at least one detector unit positioned upstream of the calibration transport path section, which at least one detector unit comprises an emitter and a detector positioned on opposite sides of the transport path, wherein the at least one detector unit is arranged to generate signal data defining a signal data curve as a sheet passes the at least one detector unit; - a processor configured for: - receiving signal data from the detector assembly; - calibrating a signal threshold by: - deriving a first signal level from the signal data corresponding to a state wherein no sheet is present between one of the at least one detector unit; - deriving a second signal level from the signal data corresponding to a state wherein a sheet covers the detector of the at least one detector unit, as seen in an emission direction from the emitter to the detector; - selecting the signal threshold to lie in between the first signal level and the second signal level; - comparing a signal data curve received from the detector assembly to the determined signal threshold to determine an intersection between said signal data curve and said signal threshold; - determining a position of a point on a sheet edge of the sheet as said sheet moves over the calibration transport section from the intersection. - receiving signal data from the detector assembly; - calibrating a signal threshold by: - deriving a first signal level from the signal data corresponding to a state wherein no sheet is present between one of the at least one detector unit; - deriving a second signal level from the signal data corresponding to a state wherein a sheet covers the detector of the at least one detector unit, as seen in an emission direction from the emitter to the detector; - selecting the signal threshold to lie in between the first signal level and the second signal level; - comparing a signal data curve received from the detector assembly to the determined signal threshold to determine an intersection between said signal data curve and said signal threshold; - determining a position of a point on a sheet edge of the sheet as said sheet moves over the calibration transport section from the intersection. - deriving a first signal level from the signal data corresponding to a state wherein no sheet is present between one of the at least one detector unit; - deriving a second signal level from the signal data corresponding to a state wherein a sheet covers the detector of the at least one detector unit, as seen in an emission direction from the emitter to the detector; - selecting the signal threshold to lie in between the first signal level and the second signal level; - comparing a signal data curve received from the detector assembly to the determined signal threshold to determine an intersection between said signal data curve and said signal threshold; - determining a position of a point on a sheet edge of the sheet as said sheet moves over the calibration transport section from the intersection.