The IBM 610 Keyboard. This is an input device; the big electric typewriter is an output device (printer). The input keyboard is not for typing in the normal sense; the keys are more like those of a scientific calculator — digits and operators. The interesting part is the circular green screen at left. This gives feedback to the operator, "echoing" the numbers as they are entered, not as digit characters, but as dots. As the operator manual says, "...a two-inch cathode ray tube for displaying the contents of the register which stands selected at any time during the operation of the machine. There are two rectangular arrays, each sixteen points wide by ten points high. Reading from top to bottom, the rows correspond to the digits from 9 through 0. The first column on the left will have a 0 spot on the face of the tube if the number being displayed is positive, and a 9 spot if the number .... is negative. The decimal point will appear as a bright spot below the digit column immediately following the point. During entry an additional spot (called the tag) will appear at the lower edge of the tube face below the digit column that is ready to receive a digit. This was, in fact, the very first screen cursor — a visual cue on a screen indicating the operator's 'current position'; the patent for it was granted in 1957. In the image above, the number so far entered is 022.37; the dot below digit 3 indicates the decimal point."