Method of operating a field device for measuring and/or monitoring at least one measurement variable (p) at an operating site and of predictive monitoring of a compliancy of at least one characteristic of said field device to a requirement specified for said field device comprising the steps of: continuously monitoring said characteristic by: at consecutive times (ti) determining a deviation (D(ti)) between a measured value (M(ti)) of a monitored variable (m) determined by said field device and a reference value (R(ti)) of said monitored variable (m), said monitored variable (m) is: a) one of the at least one measured variables (p) measured and/or monitored by said field device, b) a predefined variable determined by monitoring, diagnosing, verification or calibration means comprised in the field device, or c) is determined by the field device based on one or several input variables determined or provided by the field device and/or based on one or more input parameters determined or provided by the field device, wherein said deviations (D(ti)) are indicative of a degree of compliancy to said requirement, recording said deviations (D(ti)), applying a filter to the recorded deviations (D(ti)), based on the deviations (D(ti)) and the filtered deviations (FD(ti)) determining a noise superimposed on the filtered deviations (D(ti)), at the end of at least one monitoring time interval, during which three or more deviations (D(ti)) have been recorded and wherein none of these deviations (D(ti)) exceeded a deviation range defined for the deviations (D(ti)) based on the requirement, determining a remaining time remaining until the deviations (D(ti)) will exceed said deviation range, by: for at least two different deviation pairs (k), each comprising a first and a second deviation (D1 k (t1 k), D2 k (t2 k)) determined based on the filtered deviations (FD(ti)) comprised in the monitoring time interval, determining a simulated value (SRT k) of the remaining time by performing a Monte Carlo simulation based on the noise and the respective deviation pair (k), based on the simulated values (SRT k) determining the remaining time, and generating an output informing about the remaining time. continuously monitoring said characteristic by: at consecutive times (ti) determining a deviation (D(ti)) between a measured value (M(ti)) of a monitored variable (m) determined by said field device and a reference value (R(ti)) of said monitored variable (m), said monitored variable (m) is: a) one of the at least one measured variables (p) measured and/or monitored by said field device, b) a predefined variable determined by monitoring, diagnosing, verification or calibration means comprised in the field device, or c) is determined by the field device based on one or several input variables determined or provided by the field device and/or based on one or more input parameters determined or provided by the field device, wherein said deviations (D(ti)) are indicative of a degree of compliancy to said requirement, a) one of the at least one measured variables (p) measured and/or monitored by said field device, b) a predefined variable determined by monitoring, diagnosing, verification or calibration means comprised in the field device, or c) is determined by the field device based on one or several input variables determined or provided by the field device and/or based on one or more input parameters determined or provided by the field device, wherein said deviations (D(ti)) are indicative of a degree of compliancy to said requirement, recording said deviations (D(ti)), applying a filter to the recorded deviations (D(ti)), based on the deviations (D(ti)) and the filtered deviations (FD(ti)) determining a noise superimposed on the filtered deviations (D(ti)), at the end of at least one monitoring time interval, during which three or more deviations (D(ti)) have been recorded and wherein none of these deviations (D(ti)) exceeded a deviation range defined for the deviations (D(ti)) based on the requirement, determining a remaining time remaining until the deviations (D(ti)) will exceed said deviation range, by: for at least two different deviation pairs (k), each comprising a first and a second deviation (D1 k (t1 k), D2 k (t2 k)) determined based on the filtered deviations (FD(ti)) comprised in the monitoring time interval, determining a simulated value (SRT k) of the remaining time by performing a Monte Carlo simulation based on the noise and the respective deviation pair (k), based on the simulated values (SRT k) determining the remaining time, and generating an output informing about the remaining time. for at least two different deviation pairs (k), each comprising a first and a second deviation (D1 k (t1 k), D2 k (t2 k)) determined based on the filtered deviations (FD(ti)) comprised in the monitoring time interval, determining a simulated value (SRT k) of the remaining time by performing a Monte Carlo simulation based on the noise and the respective deviation pair (k), based on the simulated values (SRT k) determining the remaining time, and generating an output informing about the remaining time.