Hm, why have a gratuity field then.  Ah well. I wish I had that money to blow on booze.  Could pay off my student loans  
 
  
Here in the states, restaurants / bars will often automatically add in a gratuity if the party is larger than X amount of people. Thoughful of them huh? Its a common occurance that people do not notice that "service charge" and add in a tip manually, thus tipping twice.  
  
Random trivia of the day. Do you know what "tips" stands for? To Insure Prompt Service.