An electronic apparatus comprising: - a geometric fit score determining unit configured to receive a 3-D model of a patient's face and a plurality of 3-D models of patient interface devices, to determine one or more landmarks on the 3-D model of the patient's face, and to calculate a geometric fit score for each of one or more of the patient interface devices by using the 3-D model of the patient's face and the 3-D models of the one or more patient interface devices, wherein the geometric fit score determining unit is configured to fit a respective 3-D model of one of the patient interface devices to the 3-D model of the patient's face by aligning the respective 3-D model of the patient interface device with the determined landmarks on the 3-D model of the patient's face and performing a fine adjustment on the respective 3-D model of the patient interface device, wherein the patient interface device comprises a cushion and wherein the fine adjustment includes rotating and translating the 3-D model of the patient interface device to match the contour of the cushion with the contour of the 3-D model of the patient's face; - a user interface generator configured to generate a user interface (200-1,200-2,200-3,200-4,200-5) including a display area configured to display the 3-D model of the patient's face and a 3-D model a patient interface device selected from the plurality of 3-D models of patient interface devices, and a patient interface device selection area configured to display patient interface device identification information and an overall fit score which is calculated for each of the one or more patient interface devices based on the geometric fit score for each of the one or more patient interface devices and to allow a user to select the patient interface device to be displayed in the display area. - a geometric fit score determining unit configured to receive a 3-D model of a patient's face and a plurality of 3-D models of patient interface devices, to determine one or more landmarks on the 3-D model of the patient's face, and to calculate a geometric fit score for each of one or more of the patient interface devices by using the 3-D model of the patient's face and the 3-D models of the one or more patient interface devices, wherein the geometric fit score determining unit is configured to fit a respective 3-D model of one of the patient interface devices to the 3-D model of the patient's face by aligning the respective 3-D model of the patient interface device with the determined landmarks on the 3-D model of the patient's face and performing a fine adjustment on the respective 3-D model of the patient interface device, wherein the patient interface device comprises a cushion and wherein the fine adjustment includes rotating and translating the 3-D model of the patient interface device to match the contour of the cushion with the contour of the 3-D model of the patient's face; - a user interface generator configured to generate a user interface (200-1,200-2,200-3,200-4,200-5) including a display area configured to display the 3-D model of the patient's face and a 3-D model a patient interface device selected from the plurality of 3-D models of patient interface devices, and a patient interface device selection area configured to display patient interface device identification information and an overall fit score which is calculated for each of the one or more patient interface devices based on the geometric fit score for each of the one or more patient interface devices and to allow a user to select the patient interface device to be displayed in the display area.