The 'Mid' keyboard snap allows a quick and easy way select the 'Mid' point of an existing entity (middle of a line or centre of an arc/circle/ellipse).
To use this feature simply position the cursor over an entity and hit the key. If the entity is a line Draft it will display the snap symbol at the midpoint. If the entity is an arc, circle or ellipse Draft it will display the snap symbol at the centre. If a dynamic line was previously attached to the cursor this also attaches to this point. If you are happy with the point selected click anywhere in the drawing area to accept.
Use of these keyboard snaps also automatically switches to the Snap input mode.