A method, comprising: transmitting an ultrasound wave with an ultrasound emitter on a first portion of an electronic apparatus; and in response to receiving the transmitted ultrasound wave at an ultrasound sensor on a second portion of the electronic apparatus: measuring, by a measurement unit of the electronic apparatus a current propagation delay of the ultrasound wave from the ultrasound emitter to the ultrasound sensor; calculating, by a calculation unit of the electronic apparatus a current distance between the ultrasound emitter and the ultrasound sensor based on the measured current propagation delay of the ultrasound wave from the ultrasound emitter to the ultrasound sensor; and determining, by the calculation unit, a current folding angle based on the calculated current distance between the ultrasound emitter and the ultrasound sensor and further based on configuration information about the first portion and the second portion; wherein the first portion and the second portion are arranged to be foldable with respect to each other in a folding angle (α1, α2); characterized in that the method further comprises updating a displayed graphical user interface on each of the first portion and second portion based on the calculated current distance between the ultrasound emitter and the ultrasound sensor; and updating the displayed graphical user interface comprises varying a layout of a virtual keyboard drawn on the graphical user interface based on the calculated current distance between the ultrasound emitter and the ultrasound sensor. transmitting an ultrasound wave with an ultrasound emitter on a first portion of an electronic apparatus; and in response to receiving the transmitted ultrasound wave at an ultrasound sensor on a second portion of the electronic apparatus: measuring, by a measurement unit of the electronic apparatus a current propagation delay of the ultrasound wave from the ultrasound emitter to the ultrasound sensor; calculating, by a calculation unit of the electronic apparatus a current distance between the ultrasound emitter and the ultrasound sensor based on the measured current propagation delay of the ultrasound wave from the ultrasound emitter to the ultrasound sensor; and measuring, by a measurement unit of the electronic apparatus a current propagation delay of the ultrasound wave from the ultrasound emitter to the ultrasound sensor; calculating, by a calculation unit of the electronic apparatus a current distance between the ultrasound emitter and the ultrasound sensor based on the measured current propagation delay of the ultrasound wave from the ultrasound emitter to the ultrasound sensor; and determining, by the calculation unit, a current folding angle based on the calculated current distance between the ultrasound emitter and the ultrasound sensor and further based on configuration information about the first portion and the second portion; wherein the first portion and the second portion are arranged to be foldable with respect to each other in a folding angle (α1, α2); characterized in that the method further comprises updating a displayed graphical user interface on each of the first portion and second portion based on the calculated current distance between the ultrasound emitter and the ultrasound sensor; and updating the displayed graphical user interface comprises varying a layout of a virtual keyboard drawn on the graphical user interface based on the calculated current distance between the ultrasound emitter and the ultrasound sensor.