The invention relates to a portable device for measuring vertical rail measurements under service to record and report excessive vertical rail movement to prevent a train from derailing. The device may be pivoting with a tilt sensor and light-weight. The device may include a microprocessor, sensors, and a display. The device may be installed on the rail. The device may sense an approaching train, automatically turn on the device, and measure the real-time vertical displacement and the maximum/minimum vertical movement of the rail while the train is operating over the rail at all speeds.