This paper presents a method for calibrating a projector camera system consisting of a mobile projector, a stationary camera, and a planar screen. The method assumes the projector to be partially calibrated and the camera to be uncalibrated, and does not require any fiducials or natural markers on the screen. For the system of geometrically compensating images projected on the screen from a hand-held projector so that the images will always be displayed at a fixed position of the screen in a fixed shape, the method makes the projected images geometrically rectified; that is, it makes them have the correct rectangular shape of the correct aspect ratio. The method automatically performs this calibration online without requiring any effort on the user's part; all the user has to do is project a video from the hand-held projector. Furthermore, when the system makes discontinuous temporal changes such as the case where the camera and/or the screen is suddenly relocated, it automatically recovers the calibrated state that was once lost. To realize these properties, we adopt the sequential LS method and extend it to be able to deal with temporal changes of the system. We show several experimental results obtained by a real system.