Abstract: A method and apparatus for automatically calibrating the deflection of an electron beam in a graticuled cathode ray tube. The apparatus includes a microprocessor and digital-to-analog converter for generating input signals of a predetermined accuracy and sending the signals to an amplifier of a cathode ray tube to deflect the electron beam across graticule lines on the faceplate. A phototransistor optically coupled to the faceplate detects the electron beam coinciding with the graticule and in response generates an electrical signal. Signal processing circuitry processes the signal to remove noise from it and retrieve detection signals. The microprocessor receives the detection signals from the signal processing circuitry, compares each detection signal to its corresponding input signal, and adjusts the gain and offset of the amplifier in response to the comparison. Additional circuitry digitally records the beam position relative to the graticule lines.

Abstract: A counting circuit includes a digital counter for counting the pulses of an input signal during a counting interval and a pair of digital latches for latching the binary state of the input signal at the beginning and end of the counting interval, respectively. The latched binary states of the input signal and the pulse count of the digital counter are evaluated by an interpreter such as logic circuitry or a microprocessor. The interpreter resolves the pulse count into half clock cycles by comparing the binary states and in response adjusts the pulse count by the addition or subtraction of half a clock cycle.