 " Zero Sum " premiered on the Fox network on April 27 , 1997 , and was first broadcast in the United Kingdom on BBC Two on February 11 , 1998 . The episode earned a Nielsen household rating of 11 @.@ 7 with a 17 share , meaning that roughly 11 @.@ 7 percent of all television @-@ equipped households , and 17 percent of households watching television , were tuned in to the episode . A total of 18 @.@ 6 million viewers watched this episode during its original airing . 
