Abstract:It was the first time to take the maximum permissible error as the major specifications of the crustal deformation observation instrument in compiling the seismological industry standard. The specification is named the Technical requirements of instruments in network for earthquake monitoring-The instrument for crustal deformation observation. The maximum permissible error is the unique basis to judge the qualification of tilt instrument. According to the expression set from the Guide to the Expression of Uncertainty in Measurement, the judgment and the expression of the maximum permissible error of the tilt meter and strain meter have been determined. Finally,the expression of the uncertainty of measurement and the qualified judgment calculation are introduced.