Some callers use 
Chain Thru from formations such as
    Parallel Lines and want all the Centers to Trade; and all to
    Cast Off 3/4.
    We believe this is an invalid usage of 
Chain Thru since it can be
    ambiguous in several situations.  For example, from a Tidal Wave, does
    the caller want the Very Centers to Trade & then the Center 4 to Cast
    Off 3/4, or does the caller want each side to do a Centers
    Trade & all Cast Off 3/4?  Also, if 
Chain Thru is
    allowed to mean each side Centers Trade followed by all Cast Off 3/4,
    then from Twin Diamonds a 
Chain Thru could be
    interpreted as Centers of each Diamond Trade (since they are Centers
    of their 4-dancer formation), followed by confusion, since there is no
    adjacent dancer within their 4-dancer formation with whom to Cast Off 3/4. 
EN: 50