set to cooperate to form select depressions within a series of depressions the different methods of determining milling depth of each respective cutting tool is explained with examples given application_number US 98647597 A description reference is now made to the drawings where like reference numerals refer to like parts throughout the various views several embodiments of the present invention are illustrated in the various views series of depressions are illustrated as may be installed in a road by a machine having features of the present invention various cooperative milling steps as may be performed under the present invention to install a depression are illustrated conventional plunge and mill through milling procedures identified as prior art as may be performed to install a depression are illustrated for comparison to the present invention the present invention relates to installation using a milling procedure of a depression into a surface of a road in practice such depressions are installed in a series a particular series may be continuous or have a skip pattern incorporated therein fig1 depicts a continuous series 20 of depressions 22 installed in a surface 24 of a road 26 surface 24 defines a grade 28 around each depression 22 each depression 22 has a forward leading edge 30 a rearward trailing edge 32 an outer side edge 34 an inner side edge 36 and a base.