This paper describes a computer program used to compute equivalent widths via an IBM 2250 attached to an IBM 360/75J.

The measurement of stellar equivalent widths is a long tedious procedure and the final results depend to a large extent on where the stellar continuum is drawn. Therefore, a method which permits the continuum to be redrawn and the equivalent width remeasured quickly is desirable. An interactive CRT display device is an ideal instrument for allowing an astronomer to adjust the continuum level and the other parameters that are involved in equivalent width measurements. The display device discussed in this paper is an IBM model 2250 used in conjunction with a IBM 360/75J.

The “2250” consists of a 12 inch (30 cm) square CRT display tube plus a 32 function key box, an alphanumeric keyboard and a light pen which can be pointed at any illuminated spot on the screen. Thus, there are 34 interrupts that can be sensed by the program controlling the “2250”. The program that has been used communicates with the astronomer via messages and questions displayed on the CRT screen. The main program remains in a wait state until one of the 34 possible interrupts occurs, whereupon it branches to the designated subroutine and executes the procedures necessary to satisfy the interrupt.