Using a calibrated Digital Measuring Instrument, start at the beginning of the first shot with the DMI set at zero. Drive down the roadway until the DMI reads the calculated length of rock land. Stop and mark the end of the rock land. Make certain that the markings for rock lands are a different color or are somehow distinguishable from the markings used for the asphalt shots. Reset the DMI at the end of each rock land, and repeat the process.