Hi Lo Detector 12ft.  HM-417
Used for measuring pavement planeness.  Operated by one person along a highway, airport runway, or bridge surface.  The unit detects and dye-marks high and low areas that need to be ground or rerolled.  Variations are magnified 16 times on a vertical scale graduated in 1/8" increments up to 1/4".  Uses replaceable bright orange aerosol marking dye.  One case, (12) cans, comes with unit.