It surely must be me that is not communicating effectively. You are correct that when the cells I3:I14 are populated with dates, the adjusted formula works correctly as per the desired results. However, the formula is faulty when testing with the entry of NA in column I. For example, input NA into cell I15 and the returned result in E15 changes from Ready to Calib. A simular fault occurs when NA is the data for cell I9; the returned result in E9 changes from the desired result of String Check to Calib. This is the problem that I am trying to correct.