NOTE 1 A method of checking true r.m.s. indication is described in Annex A. This method is mainly retained for instruments not based on modern analogue to digital conversion and numerical calculation of r.m.s., but can also be applied to instruments which are so based.

NOTE 2 Subject to adaptation of the measurement frequency range, these instruments can be used for other applications where similar accuracy of measurement is required, measurement of vibration velocity of structures, tunnels, bridges, etc. Optionally phase measurements may be included.