How to display radius while adding element in ArcObject?

I want to display the radius of drawing circle when user adds this figure on the map.

1. User clicks on the icon.


2. 
   

   Then user begins drawing circle (I process the MouseDown event)

   
   

   IGeometry geom = Map.TrackCircle();

   
   


3. 
   

   When user clicks on the map, I draw this circle on the map (I get radius from TrackCircle and center from mouse coordinates).

   
   

I want to display radius on the map or in the bottom tooltip (like ArcMap) on the step 2 (TrackCircle).

I think I must process the event OnAfterDraw of the MapControl, but I do not know how (how can I know that user drawing circle and the radius of this circle?).