Up time. The time it takes for a sample of rock cut from a [[formation]] by the drilling [[bit]] to be carried from its depth of origin to a location on the surface, where it is collected. Lag time is calculated by subtracting [[down time]] from the total time it takes for a marker, introduced into the drilling mud at the surface, to travel to the bottom of the borehole and back to the surface where it can be detected or collected.