This International Standard defines terms relating to geodetic field instruments only, e.g. distance meters, levels, theodolites and others, and their essential component parts which are normally used in terrestrial measuring operations of ordnance survey, topographic survey, plane survey and engineering survey. Therefore terms concerning fields such as the following are not mentioned, e.g. photogrammetry, astronomy, hydrographic survey and industrial metrology. Accessories which are not necessary for the functioning of the instruments are not dealt with. The terms are arranged in English alphabetical order. For practical reasons, terms in lightface type marked with an asterisk (*) are explained only in a note or in the context of the definition of another term. These terms can also be found in the alphabetical index. NOTE In addition to terms and definitions used in two of the three official ISO languages (English and French), this International Standard gives the equivalent terms in the German language; these are published under the responsibility of the member body for Germany (DIN). However, only the terms and definitions given in the official languages can be considered as ISO terms and definitions.