This great compass companion measures altitude from 0¨C 15,000 feet and barometric pressure from 17¨C 31" Hg. It is protected by a hard side case, Size: 2 3/4" x 3 1/2" x 1".  This instrument is a necessity for geologic mapping especially where a suitable topographic map is not available or specific altitudes are required to complement compass bearings and topographic location.