PURPOSE: To enable an operator to retrieve easily the discrimination code of a data point by indicating the data point on a CRT system chart to know the discrimination code.

CONSTITUTION: When the discrimination code of a data point is desired, a cursor display on a system chart of a CRT screen 22 is shifted onto the position of a desired numeric character by a shift key 32. Then a prescribed interruption key 33 is pushed to send an interruption to a computer 10. The computer 10 reads the position indicated by the cursor and extracts the animation display information out of an information store buffer 6 to retrieve a screen unit number corresponding to a position on the screen. Then the discrimination code of data point is obtained out of a reference data point discrimination code definition memory 4 according to said retrieved unit number and the screen number which is under display. Thus the name of the data point is obtained and transmitted to a refresh memory 21 of a CRT device 20 together with the discrimination code for display at the lowest line of the CRT system chart screen under display.