twSet2Click( nDblTime )
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     Set the default time to wait for a Double Click  to occur. This
     time is used as  the default wait time for twM2Click(). If no
     parameter is passed, the current setting is returned.

       Arguments:

     nDblTime - 'N' The time to use as a default for the double click
                    wait period. Initially it is a half second.

       Return:

     The old time.

       Example:

     nDoubleTime := twSet2Click()