|Draft → Utilities → Flip Dimension|
When in 2D mode, the text of the Draft dimensions is displayed aligned to the dimension line. The Dimension tool always tries to show you the dimension text on the correct side of the dimension line, depending on where you are viewing it from. In some cases, though, the viewing direction might not reflect the intent of the viewer, and the orientation of the dimension text might be inverted. This tool inverts that orientation on selected dimension objects.
What this tool does, internally, is to invert the Normal direction of the dimension, which is the direction used to draw the text with the correct orientation. Dimensions also have a Flip Text property, which rotates the text by 180 degrees around the normal direction. By combining these two features, normal direction and Flip Text, you are able to make the text appear correctly in all possible situations.