To draw an arc from a center point, use the Arc by Center tool. Indicate a center and then drag the cursor to indicate the radius, just as though you were creating a full circle. After that, however, use the radius indication as the start angle of the arc, and a third indication gives the end angle. When moving the cursor for the third location, the Arc can be created in either direction from your second location. However, once the Arc being rubberbanded exceeds 90°, that locks in the direction from the second location, allowing you to continue moving the cursor to create Arcs greater than 180° if desired.