Digital read out
A digital readout (DRO) is a numeric display, usually with an integrated keyboard and some means of numeric representation. Its integral computer reads signals generated by linear encoders or (less frequently) rotary encoders installed to track machine axes, using these measures to keep track of and display to a machine operator the workpiece position (e.g., milling machines), or tool position (lathes, grinders, etc) in space.
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In machine-shop terminology, the complete Digital Read Out system (consisting of a computer, axis-position encoders, and a numeric display) is referred to by the acronym DRO. Such a system is commonly fitted to machines in today's shops, especially for metal working — lathes, cylindrical grinders, milling machines, surface grinders, boring mills and other machine tools — to allow the operator to work faster and with greater accuracy. Use of DROs is not limited to manually operated machines. CNC machines can usually be switched to manual operation, and in this case a form of DRO is simulated on its control panel.