The present invention is directed toward a residual life indicator. A second mask of the set, for example a trimming mask, which is assigned to the first mask, can have a semitransparent region assigned to the structure element of the first mask. The drag mechanism includes: drag-handling unit that screws onto the fore end of the spool shaft; and friction unit disposed so as to contact the rear face of the rear flange. Each of the content management systems comprises content. The vapor conduits communicate at upper ends thereof with the production well, so that vapors that do not reflux are collected in the production well and are transmitted to the surface for processing. The users may also issue other commands requesting information such as the latest spoken word indicating location, the latest spoken word indicating time, the latest spoken word indicating method, etc.