To carry out a covermeter survey, NDT personnel often have to input the bar diameter on their covermeters on site without knowing the actual diameter of the reinforcing bar in the concrete. This is especially the case when surveying older structures. Using a default setting for the bar diameter such as 12mm or 16mm will not produce concrete cover readings as accurately as indicated in the previous section. In order to measure concrete cover in the most accurate manner, the bar diameter needs to be known and set accordingly in the covermeter. However it is interesting to consider how large an affect an educated “guestimate” would have on the accuracy of cover measurements.