I cannot tell what Torfinn advises as its just a static image of a workplane, when I view it.
Anyway. Murrays approach is a lot quicker than my long way. But one 'long winded' approach is. Show workplane on. Workplane by entity on the dimension. Edit workplane tool and using handles rotate 180 degrees. select dimension, place on workplane. As I say its not the quickest method, and may crash if done it is too often.
What it sounds to me like Murray is suggesting. select the dimension and make a mental note of its x and y axes directions (example x pointing right, Y pointing up). Workplane by 3 points, snapping the x and y at 180 degrees from those noted earlier, (snapping x pointing left and y pointing down). place on workplane.