why not look up Cross in the help file?
  
 d
          I get an error when I run the following, this line is taken directly from    the online reference (reproduced below). The error I get is "too many    arguments"
Sell =    Cross( Study( "SU" ), Close, GetChartID() );
What is the correct    format for using this?
Best regards,
-VJ
  
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   Write the formula that checks trend line break 
   In this example we will detect if the closing price drops BELOW support    trend line. This is actually very simple:
        sell = cross( study( "SU" ), close, GetChartID()    );
   Note that study() function accepts two arguments: the first is StudyID    two letter code that corresponds to one given in properites dialog; the second    argument is chart ID - it should be taken either via GetChartID() function    (then it refers to current indicator) or read from 
Parameter dialog, Axes & Grid: Miscellaneous:    Chart ID
       
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