Machining accuracy refers to the similarity of measurements after multiple attempts or between multiple copies of a part.
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In other words, a machine is highly accurate if it hits exactly the same point on multiple copies of a part.
This is different from accuracy because accuracy is not specifically concerned with whether the "points" are the same as those specified in the design! A machine can be so precise that it always cuts 3 mm to the left of the intended mark.
Obviously, it is important to be both accurate and precise.
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Accuracy means that you are reaching the coordinates specified in the design, while precision means that you are hitting them consistently over multiple units.