50-73-206: Maps to be updated on basis of semiannual surveys.

An extension of the last preceding survey of every mine in active operation shall be made once every 6 months, and the result of the survey, with the date, must be promptly and accurately entered upon the original maps to show all changes in plan or new work in the mine and all extensions of the workings to the most advanced boundary of the workings that have been made since the preceding survey.