High precision geometric levelling

An altimetric survey is carried out using sub-millimetre precision optical levels and invar staff to define in detail the altimetry of a site, inside or outside a building, and is particularly useful for defining a differential settlement framework corresponding to a floor of a historic building, or as a monitoring activity for assessing subsidence, if repeated at pre-determined time intervals. Finally, this method of measurement is carried out in the case of load tests, when the intrados of the floor subjected to the load are inaccessible and one wishes to read the absolute deflections, operating only from the extrados. When carrying out altimetric monitoring, it is advisable to take as a reference point a point outside the range of possible vertical displacements, considered as a fixed point, in order to compensate for any measurement errors.