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     Although maps can be drawn without attention to elevation, high points have frequently been used to determine location. With the development of countour mapping altitude is plotted as well as latitude and longitude. One of the most convenient ways to determine elevation of altitude is to use an aneroid barometer with measures changes in air pressure. The barometer can be calibrated to read directly in feet or meters above sea level. The stamps shows a pocket aneroide barometer.
     The other instrument measures vertical angles, and is used as the astrolabe, quadrant, cross staff, back staff, and sextant to measure the angle of a star above the horizon to determine latitude.