nevertheless important to maintain an observation book although it will serve for control purposes rather than for direct data recording. 3.4 Mechanical Recording Instruments As already mentioned, there are physical principles available for measuring meteorological parameters, which result in changes of the length of the sensing element or where the sensor exerts a force. This can be transmitted mechanically with or without amplification to a recording system, which is usually based on a clock driven paper strip, either of the drum or endless belt type. With regard to the magnitude of the movements and/or the exerted forces and the technical possibilities for mechanical amplification, mechanical recorders have a limited accuracy and the distance between the sensing element and the recording device has to be kept small. The main advantage of mechanical recorders are the
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