Abstract: Multiple vehicles located within a predefined search space are located and tracked using at least two spaced-apart transmitters. Each transmitter can broadcast an omnidirectional initialization signal and a positioning signal having a null or break in its wavefront. By rotating the positioning signal, the null will sweep the predefined search space and by detecting both the initialization signal and the null in the positioning signal, the position of each vehicle can be determined. In the preferred embodiment, the locational information from each vehicle is collected at a central location, typically in a data acquisition system or controller. In the particularly preferred embodiment, the locational information is further relied on to provide for command information for feedback control of the vehicles.

Abstract: This invention relates to documents, such as banknotes, which are produced and used in large numbers and which, for a given series, are identical one with another except for a unique multi-digit number upon each individual document, the number thus uniquely identifying that document within the series. According to the present invention, to render unauthorized reproduction of the document more difficult, on each document, at least two characters in the identifying number differ from each other (in addition to any differences in the letters or digits which they represent) in one or more visible characteristics. Thus the differing characters may have different heights or widths or be in different styles of type. Preferably, the identifying number appears twice on each document, in diagonally opposite corners, and preferably the variation of physical characteristics of the characters along the length of one of the numbers is reversed in direction in the other of the numbers.

Abstract: This invention relates to documents, such as banknotes, which are produced and used in large numbers and which, for a given series, are identical one with another except for a unique multi-digit number upon each individual document, the number thus uniquely identifying that document within the series. According to the present invention, to render unauthorized reproduction of the document more difficult, on each document, at least two characters in the identifying number differ from each other (in addition to any differences in the letters or digits which they represent) in one or more visible characteristics. Thus the differing characters may have different heights or widths or be in different styles of type. Preferably, the identifying number appears twice on each document; in diagonally opposite corners, and preferably the variation of physical characteristics of the characters along the length of one of the numbers is reversed in direction in the other of the numbers.