Edit Bar control: Ok
This tool adds a concentric constraint between two circular arcs or an arc and a point.
To use the tool, identify two arcs or an entity point and an arc. When you have finished identifying them the arcs (and the entity point where applicable) will be constrained so that they have a common centre point. (The entity point will be at the same location as the arc centres).
After creating the concentric constraint you can hover your cursor over the constraint and all related entities will be highlighted.
Shift Modifier
You can also hold the Shift key down whilst identifying them to include more arcs and points. When you have finished identifying them, all arcs and points will be included in the constraint.
After identifying two arcs, or an arc and a point, whilst using the Shift modifier the Ok button becomes active on the edit bar: 
You can now click this button to finish the tool and apply the constraint.
Pre-selected Entities
Alternatively, you can select two or more arcs and then start the tool. The concentric constraint will then be added to all selected arcs.
NOTE: Whilst this tool can be used to move points and entities so as to satisfy the constraint, it is recommended that entities are created in the desired position.