The 'Tan' keyboard snap allows a quick and easy way select a 'Tangent' point on an arc/circle. This snap is only valid therefore if a current point exists i.e. selecting the second point when drawing a line.
To use this feature simply position the cursor over an arc/circle and hit the key. If a tangency point exists Draft it will display the snap symbol at the nearest tangency point. The dynamic line previously attached to the cursor also attaches to this point. If you are happy with the point selected click anywhere in the drawing area to accept.
Alternatively you can hit the 'R' key to define a position Relative to this point, or hit or to select the X or Y values of this point.
Use of these keyboard snaps also automatically switches to the Snap input mode.