Ohio Revised Code Title III. Counties § 315.15

When a county engineer or his deputy is called upon to make a survey to be offered as evidence, the adverse party having notice of the time of the making of such survey, the county engineer or deputy, upon application of either party to the cause of action, shall administer an oath to any witness brought to prove any corner or line of such survey, or the existence of any natural or artificial object or mark which is necessary to identify any corner or line of such survey. Such testimony shall be reduced to writing, subscribed by the witnesses, and return thereof made to the court with the return of the survey.