Note: On some vehicles - specifically trucks, the OBDII adapter will not report the proper speed to the DMI display, resulting in lower than actual distances measured. For the vehicles on which this problem has been observed, the distance recorded will be less than 10% of actual. The average survey can be completed simply by using the four large keys on the left side of the instrument. Ideal for measuring highways, school bus routes, telephone pole spacing, gas pipelines, E-911 addressing, cable TV length, postal routes, railway length, field crop length, etc. Features include non-volatile, unlimited internal memory for storing numerous events along with the distance they occur; auto calibration memory for up to 4 vehicles; speed trap function; unlimited event memory for inventory, including event names; special functions for computing material needs (area, volume, tonnage); back-lit keypad and display; and an interval distance display for logging distance between events. A sensor and a vehicle installation kit or appropriate cable kit are required for use (sold separately).