Abstract: A device for freeing an area of birds, insects, or other pests which simultaneously emits two separate audio frequencies which are shifted periodically. The device comprises two separate oscillators whose output signals are mixed together at the input of a power amplifier driving a loud speaker. The frequency of each oscillator can be independently adjusted. A resistive load is placed in the common power supply line of the two oscillators and is periodically shunted in order to shift the frequency of both oscillators. The periodical shunting of the load is accomplished by a SCR switch driven by a third oscillator having a very low frequency. The resulting dual frequency pulsating signal can be adjusted with wide ranges of frequencies in order to deter various types of animals from frequenting the area.

Abstract: A scale including a rectangular base frame supporting on opposite sides horizontally disposed torsion bars having their central portions secured to said frame and including a horizontal, plate-like rectangular platform superposed to said frame and bars. End portion of said bars support said platform by upstanding, threaded members engaged in said bars, eccentric seats on threaded member heads, and balls on said seats on which the platform rests. General platform leveling can be achieved by full-turn rotation of the threaded members and scale calibration adjustment can be facilitated by less than full-turn adjustment of said threaded members thereby shifting the locations of the balls along the torsion bars. Each torsion bar end portion has an upper and a lower strain gage for a total of eight. Two modified Wheatstone bridges use the strain gages for all resistors of the bridges whereby all bridge resistors are active and the two bridges form the sole electrical means to measure load on the scale.