Wyo. Stat. § 30-3-109: Check-in and check-out system.

Each mine shall have a check-in and check-out system that will identify every individual underground. An accurate record of persons in the mine consisting of a written record or a check board shall be kept on the surface in a place that will not be affected in the event of an explosion. The record shall bear a number identical to the identification check carried by the person underground.