The referencing or alignment of a checking fixture can be done in two different ways: geometric system or 3 points system.

The term Geometric refers to the alignment system composed of plan, straight line, point. On a mathematic point of view, this system is the most correct. For this system, you need to have enough elements to create a plan, a straight line and a point, and to define their nominal position. When using three sights or three rectified bushings, the centres of these elements have to be measured; the plan will be made thanks to these three elements, the straight line thanks to two of them, and finally one of them will be used as a reference point.

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