A calibration method for a knob applicable to a touch panel, the knob comprising at least one sensing pad, the calibration method comprising: obtaining at least one sensed position of each sensing pad of said at least one sensing pad by sensing a position of said each sensing pad through the touch panel; and calculating a position of a center of the knob by using a formula of a radius of a circumscribed circle according to said at least one sensed position of said each sensing pad; wherein said at least one sensed position of said each sensing pad comprises multiple sensed positions that are obtained in response to a touch and rotation event of the knob; characterized in that the knob comprises only two sensing pads (120A, 120B), and calculating the position of the center of the knob by using the formula of the radius of the circumscribed circle according to said at least one sensed position of said each sensing pad (120A, 120B) comprises: sensing rotation tracks of the two sensing pads (120A, 120B) according to sensed positions of the two sensing pads (120A, 120B), respectively, wherein a total track formed by summing up the rotation tracks of the two sensing pads (120A, 120B) traverses at least a quarter circle of the knob; arranging the total track as a movement track of the two sensing pads (120A, 120B); and calculating the position of the center of the knob by using the formula of the radius of the circumscribed circle according to the movement track; wherein an overlapped part of the two rotation tracks is considered as one rotation track. obtaining at least one sensed position of each sensing pad of said at least one sensing pad by sensing a position of said each sensing pad through the touch panel; and calculating a position of a center of the knob by using a formula of a radius of a circumscribed circle according to said at least one sensed position of said each sensing pad; wherein said at least one sensed position of said each sensing pad comprises multiple sensed positions that are obtained in response to a touch and rotation event of the knob; characterized in that the knob comprises only two sensing pads (120A, 120B), and calculating the position of the center of the knob by using the formula of the radius of the circumscribed circle according to said at least one sensed position of said each sensing pad (120A, 120B) comprises: sensing rotation tracks of the two sensing pads (120A, 120B) according to sensed positions of the two sensing pads (120A, 120B), respectively, wherein a total track formed by summing up the rotation tracks of the two sensing pads (120A, 120B) traverses at least a quarter circle of the knob; arranging the total track as a movement track of the two sensing pads (120A, 120B); and calculating the position of the center of the knob by using the formula of the radius of the circumscribed circle according to the movement track; wherein an overlapped part of the two rotation tracks is considered as one rotation track. sensing rotation tracks of the two sensing pads (120A, 120B) according to sensed positions of the two sensing pads (120A, 120B), respectively, wherein a total track formed by summing up the rotation tracks of the two sensing pads (120A, 120B) traverses at least a quarter circle of the knob; arranging the total track as a movement track of the two sensing pads (120A, 120B); and calculating the position of the center of the knob by using the formula of the radius of the circumscribed circle according to the movement track; wherein an overlapped part of the two rotation tracks is considered as one rotation track.