Abstract: An interactive display device is of the type which displays data and allows an operator to input fresh data and/or change the data that is displayed. The data is displayed by a plurality of arrays of discrete display elements each of which can be independently driven to produce an optical output, and the interactive input is by means of a light pen or "wand" which detects light and which the operator points at the display element associated with the data to which the desired input relates. Driver circuit means scan the arrays of said plurality thereof simultaneously with signals which determine whether each display element is in the ON or OFF state. These scanning signals include coded pulses the coding of which is representative of the particular array being scanned thereby. Means for inputting data comprise said light pen and associated circuit means operative to identify the coded pulses and thus identify the array containing the selected display element.

Abstract: A navigational aid enables the effect of a course and/or speed alteration of one vessel on the nearest possible approach distance of another vessel to be calculated, using data readily obtainable from a simple relative radar display on said one vessel. The aid comprises a plurality of sealed manually-settable means for individually setting in data inputs respectively representative of the following:(1) the minimum nearest approach distance if no course or speed change is made;(2) the range of said other vessel;(3) the present speed of said one vessel;(4) the proposed course alteration;(5) the proposed speed alteration; and(6) the time for which the proposed course and speed will be held.The aid further comprises means to compute from the foregoing input data the resultant nearest possible approach with the proposed manoeuvre, and indicating means to provide an indication of said resultant nearest possible approach.