Variable accuracy trend graph display apparatus

Abstract

A graph display apparatus using a CRT display unit of raster scanning type for displaying a graph with a high accuracy, that is, a high resolution. The apparatus comprises a raster counter for counting the number of rasters to identify the raster number of the scanning lines presently scanning the display screen of the CRT display unit, and a plurality of graph display units for displaying a graph with a standard accuracy. Each graph display unit comprises a memory having a capacity corresponding to the number of time points obtained by dividing the time axis extending in the scanning direction of the raster on the display screen by the number n of data plotting for storing the raster numbers corresponding to the levels of the quantities to be displayed at the individual time points, and a comparator comparing the output of the raster counter with the output of the memory read out sequentially in timing relation with the individual time points for providing a coincidence detection signal only when coincidence is reached between the output of the counter and the output of the memory at a time point. The display signal outputs of these graph display units are combined to display a graph with a desired resolution which is for example two or four times the standard resolution. To this end, a variable accuracy circuit is associated with each of the graph display units to receive the output of the associated graph display unit thereby providing a display signal output at the timing of scanning specific dots among a plurality of dots corresponding to one time point. The outputs of the variable accuracy circuits are applied to an OR circuit which applies an output signal representing the logical sum of these inputs to the CRT display unit.