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 Create a best fit broadcast gfile and tfile with partials
  
 Usage:  sh_bcfit  -f <nav-files> -d <year doy> -o <orbit-name>
  
  <nav-file> RINEX navigation file  (required)
 
  <year doy>  year and day-of-year; if omitted, day and span taken
              from session.info
 
  <orbit-name> 4-character code for output t-file; default, taken from 
               nav-file name, e.g., tbrdc[y].[ddd] 
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