Abstract: Each data point within a two-dimensional code can be represented by a distribution of spots. Each spot can be made small enough to be invisible to the human eye so that the two-dimensional code can be invisible on or within transparent or nontransparent materials. The spots can be spaced at a large distance to increase the signal-to-noise ratio for an optical code reader. A code reader can be adapted to read the spots and determine the data points.

Abstract: Each black square within a two-dimensional code can be represented by a distribution of spots. Each spot can be made small enough to be invisible to the human eye so that the two-dimensional code can be invisible on or within transparent or nontransparent materials. The spots can be spaced at a large distance to increase the signal-to-noise ratio for an optical code reader. A laser can be used to produce the spots.

Abstract: Each data point within a two-dimensional code can be represented by a distribution of spots. Each spot can be made small enough to be invisible to the human eye so that the two-dimensional code can be invisible on or within transparent or nontransparent materials. The spots can be spaced at a large distance to increase the signal-to-noise ratio for an optical code reader. A code reader can be adapted to read the spots and determine the data points.

Abstract: Each black square within a two-dimensional code can be represented by a distribution of spots. Each spot can be made small enough to be invisible to the human eye so that the two-dimensional code can be invisible on or within transparent or nontransparent materials. The spots can be spaced at a large distance to increase the signal-to-noise ratio for an optical code reader. A laser can be used to produce the spots.

Abstract: An ultrasonic angular measurement system is disclosed. The system is comprised of three parts, a control box used to collect and process data, an ultrasonic transducer, and a reflector block. The reflector block is configured so that it intercepts transmitted pulses received over a wide range of angles back to the transducer. All the components are self contained within a transportable housing which is attached to the aircraft deck during measurement of tip-off angle. The range of angle measurement is permitted because of the use of the unique reflector block which comprises a plurality of reflector segments for reflecting ultrasonic pulses transmitted at various ranges of angles.