Calibration device for carrying out a disassembly method for gas turbines for replacing and/or inspecting and/or repairing components arranged in a front bearing region of the gas turbine, wherein - the gas turbine comprising at least one fan module, a gas turbine housing, a low-pressure system and a high-pressure system, wherein - the low-pressure system comprising a low-pressure compressor, a low-pressure turbine, a connecting shaft, a flanged shaft and a N1 shaft, wherein - the N1 shaft being connected to the low-pressure compressor via the flanged shaft and the connecting shaft, wherein - the connecting shaft being supported in the gas turbine housing via a first bearing unit, and - the flanged shaft being supported in the gas turbine housing via a second bearing unit, wherein - the disassembly method comprises at least the steps of: a) dismounting the fan module, and b) fixing the N1 shaft in an axial direction relative to the gas turbine housing using a fixing device, and c) dismounting the flanged shaft using a guide device, the orientation of which relative to the gas turbine in at least one spatial direction is determined by a component of the remaining gas turbine, this taking place after the N1 shaft has been fixed and after the fan module has been dismounted, wherein - in method step c), the flanged shaft and the low-pressure compressor are dismounted, wherein - in method step c), the first bearing unit and the connecting shaft are also dismounted, this taking place after the low-pressure compressor has been dismounted, wherein - following the method steps a) to c), an additional method step 1) is provided for replacing at least one sub-system of a sensor system, wherein - the method step 1) also includes the calibration of the sensor system, wherein - the sensor system substantially comprising a sensor and a clock generator, wherein - the distance between a clock generator and a sensor head being measured during calibration using the calibration device, characterised in that - the calibration device comprises a first and second cylinder-shaped outer face (23, 24), wherein - the first cylinder-shaped outer face and the second cylinder-shaped outer face are arranged concentrically to each other, - a radius of the first cylinder-shaped outer face corresponds to the radius of a clock generator of the sensor system, and - the second cylinder-shaped outer face corresponds in shape to an inner face of the second bearing unit. - the gas turbine comprising at least one fan module, a gas turbine housing, a low-pressure system and a high-pressure system, wherein - the low-pressure system comprising a low-pressure compressor, a low-pressure turbine, a connecting shaft, a flanged shaft and a N1 shaft, wherein - the N1 shaft being connected to the low-pressure compressor via the flanged shaft and the connecting shaft, wherein - the connecting shaft being supported in the gas turbine housing via a first bearing unit, and - the flanged shaft being supported in the gas turbine housing via a second bearing unit, wherein - the disassembly method comprises at least the steps of: a) dismounting the fan module, and b) fixing the N1 shaft in an axial direction relative to the gas turbine housing using a fixing device, and c) dismounting the flanged shaft using a guide device, the orientation of which relative to the gas turbine in at least one spatial direction is determined by a component of the remaining gas turbine, this taking place after the N1 shaft has been fixed and after the fan module has been dismounted, wherein a) dismounting the fan module, and b) fixing the N1 shaft in an axial direction relative to the gas turbine housing using a fixing device, and c) dismounting the flanged shaft using a guide device, the orientation of which relative to the gas turbine in at least one spatial direction is determined by a component of the remaining gas turbine, this taking place after the N1 shaft has been fixed and after the fan module has been dismounted, wherein - in method step c), the flanged shaft and the low-pressure compressor are dismounted, wherein - in method step c), the first bearing unit and the connecting shaft are also dismounted, this taking place after the low-pressure compressor has been dismounted, wherein - following the method steps a) to c), an additional method step 1) is provided for replacing at least one sub-system of a sensor system, wherein - the method step 1) also includes the calibration of the sensor system, wherein - the sensor system substantially comprising a sensor and a clock generator, wherein - the distance between a clock generator and a sensor head being measured during calibration using the calibration device, characterised in that - the calibration device comprises a first and second cylinder-shaped outer face (23, 24), wherein - the first cylinder-shaped outer face and the second cylinder-shaped outer face are arranged concentrically to each other, - a radius of the first cylinder-shaped outer face corresponds to the radius of a clock generator of the sensor system, and - the second cylinder-shaped outer face corresponds in shape to an inner face of the second bearing unit.