The number of Marine casulaties on Battle.net is an approximation incorporating several educated guesses about Starcraft games hosted there. Based on the number of players reported playing Starcraft at normal times each day, I've estimated that about 100,000 games are started by Terran players each day (on average). Of those games, I've made a conservative guess that each such player loses about 25 Marines in a typical game. These figures are multiplied by the overall number of days since the release of the Starcraft game. The total number is updated every second. If you somehow have more accurate information about these parameters, please don't hesitate to email me and get this counter fine-tuned!