Plumbing. When the ground is covered by obstacles, weeds, low brush, and irregularities in the ground surface, it will be difficult or impossible to lay the tape on the ground during measurement. Both ends of the tape should be held above ground (about the level of the waist or chest) and in a horizontal position. Also, each end of tape is marked by positioning a plumb line (defined by a plumb bob and string) held by both tapemen.