Edit Bar controls: Fixed Text, Both ends, Align dimension, Dimension Mode, Text mode, Width, Height, Settings, Favourites.
This tool allows you to dimension horizontal distances between two points. These points can lie on the same entity or different entities.
See Dimension General for standard Edit Bar controls.
Pick the first point. A flexible dimension, comprising a projection line, dimension line and text outline is drawn. Pick the second point defining the dimension.
Again a flexible dimension is drawn, this time with two projection lines, allowing you to fix the position of the dimension line.
When picking the points, you should be careful to use an appropriate snap mode to ensure the dimension is placed accurately.
See Snap Modes and Lock Modifiers.