The source of any legal or survey monuments must be documented on the face of the survey. If the source or origin is uncertain, the (OU) origin unknown notation is made. Every effort is generally made by surveyors, in the field, to identify who set each iron bar by viewing the unique Surveyor Number inscribed thereon. Monuments whose origin has not been ascertained, may still be used in boundary re-establishment, however, must be noted as such.