Day of the Week Effect in Small Securities Markets

Levelling systems (e.g., scrapers) are laser-controlled by use of a sending station emitting a rotating, pulsed, laser beam in a plane either horizontal or inclined relative to the horizontal and a receiving station at the scraper which has a mast carrying one or more sensors. The sensor signals either signal the operator to raise, lower or change the angle of the blade or control the blade by hydraulic or electric actuations. The same mast mounted on a scraper (with blade raised to inoperative position) or other vehicle may be used for surveying a field. It is necessary in either case to raise and lower the mast so that the sensor intercepts the laser signal. This has heretofore been done in various ways hydraulically, electrically or mechanically (e.g., worm drive). The present invention provides an electrically driven mast having a brake which opposes the tendency of other electrically operated masts to overtravel when descending, which tendency is attributable to the inertia resulting from the weight of the moving elements of the mast. The brake releases when the mast is being raised.