Abstract: An altimeter has a pointer which rotates clockwise once round a dial for each thousand unit (feet or meters) increase in altitude, the zero of the dial being in the nine o'clock position.Two digital displays are situated one above and one below the horizontal through the dial zero. When the pointer lies in the upper segment of the dial a reading is shown on the upper display and when the pointer lies in the lower segment of the dial a reading is shown on the lower display. When the pointer is in the region of the zero position (for example within 100 feet of the zero position) a reading is shown on both displays. The upper display then reads thousands corresponding to a pointer position above zero and the lower display reads thousands corresponding to a pointer position below zero (whether the pointer is above or below zero).