What is a SketchUp dimension?
SketchUp dimension entities are finite lines with length information allowing you to quickly and effectively communicate key dimensions of your model. Dimensions can move and update automatically as you make changes to your model. Dimensions are drawn with the built-in Dimension Tool. The link between geometry and dimensions is unidirectional: if you change the value of a SketchUp dimension, the model is not updated. So SketchUp dimensions are only used to retrieve length information from your model.