This Nordtest method specifies a methodology and a measuring device (the ”Bow- meter”) for carrying out field measurements of dimensional changes and deformation of natural stone panels used as exterior cladding . The method represents a tool for the inspection and assessment of status and prediction of further development on existing facades where damage in the form of bowing of natural stone panels has been observed. This phenomenon is experienced occasionally on crystalline marble  used as exterior cladding.
Risk analysis, together with the purpose of each specific inspection and assessment and the accessibility of suitable measurable panels will govern and influence the extent of the field measurements.
The method does not deal with the causes of bowing or other kinds of changes in the cladding material, but it does give some guidance on the evaluation of the results. Further laboratory analysis  of panels demounted from the façade may be necessary in order to evaluate if bowing indicates e.g. strength loss in the material. When possible the laboratory analysis should also include measurements on unexposed (spare) panels.
The methodology is illustrated in Annex A for an Introductory Assessment level. In addition, some suggestions are given for how the results may be discussed in order to give recommendations for further action.