This system is an electronic navigation aid known as a plotter. It is used in conjuntion with marine charts to keep track of position, calculate range & bearing etc. A major feature is its ability to link to other navigational systems, particularly GPS, when it can be used either to plot the measured position on the chart or can be used to send waypoint positions to the GPS etc.
Technically, it is a digitiser linked to a computer. By a simple 3-point procedure, it can be calibrated to any chart so that it can then read in latitude and longitude. Entering a waypoint to a navigational system is then simply a case of moving the cursor to it and clicking the button. Plotting position from a GPS is done using a set of four lights arranged around the cursor. They respond to cursor position in comparison to the GPS position, showing which way to move the cursor to reach the measured point.
From more information on the Yeoman product: Yeoman PLC