WaitMouseUp
 After receiving a mouse-down event, you can use the WaitMouseUp function to determine if the user subsequently released the mouse.
FUNCTION WaitMouseUp: Boolean;
DESCRIPTION
 The WaitMouseUp function looks in the Operating System event queue for a mouse-up event. If it finds one, the WaitMouseUp function removes the mouse-up event from the queue and returns TRUE. If it does not find any mouse events pending in the Operating System event queue, the WaitMouseUp function returns FALSE.
SEE ALSO
 See "The Event Queue" on page 2-83 for information about the Operating System 
event queue.