SmartDraw can show the length of any wall segment using blue extension lines that are offset from the wall itself. You can choose to show or display these extension lines using the Dimensions dialog accessible under the Design tab.
This dialogs lets you set preferences about other display options related to dimensions.
You can choose not to show dimensions or only show them when an object is selected.
You can also choose to simply float the dimension next to a wall or use extension lines to show the exact segment a dimension refers to. By default, dimensions will always be on using extension lines.
In some cases, extension lines may cause some visual clutter. You can move the lines using a black diamond shape near where the dimension is displayed. Click the diamond shape and drag it to the move the extension line closer or farther away from the wall.