Prior to logging of a process flags for locking at all addresses of a logging area of a tag are set to state 1 by means of an interrogator. A high limit (h) and a low limit (l) of an interval (l-h) of such values (v) of a physical parameter are determined, which are proper for preserving usability of a tagged article. Said values (v) acquired with a sensor and acquisition times related thereto are converted into less numerous data characterizing the process by observing said limits (h, l). Said data characterizing the process are logged in said logging area. Said process log cannot be modified in any way at a later stage. The invention also provides for an efficient observation of longer period of the process in the tagged article in order to inspect the usability thereof.