Abstract: Offset-error included data normally is output from a single ramp analog to digital converter in response to input information applied thereto during light or cuvette sample intervals. During dark sample intervals between the cuvette sample intervals, the input information is blocked from the converter and the converter is operated with the output counter counting down to a dark count representing the offset error of the counter. During the next cuvette sample interval the counter counts up from the dark count effectively subtracting out the offset error introduced by the converter.

Abstract: A security device for an electronic calculator consists of an electronic circuit within the calculator which permits operation of the calculator only after the operator has correctly operated a predetermined sequence of keys. The circuit is connected to the sense and the digit drive lines of an electronic calculator having an electronically scanned keyboard. The circuit includes a key selection matrix, a valid actuation discriminator logic, an actuation sequence counter, an alarm inhibiter and an alarm which disables the proper functioning of the calculator.