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SketchUp features a geometric analysis engine, called the inference engine, allowing you to work in 3D space using a 2D screen and input device. This engine helps you draw very accurately by inferring points from other points as you draw while also providing you with visual cues.
The inference engine uses visual cues, appearing automatically while working on the model, to identify significant points or geometric conditions. These cues make complex inference combinations clear to you as you draw.
Additionally, the inference engine uses specific colors to indicate its type of inference (covered further in Inference Types).