A second officer's log was the main log kept by the second officer aboard a starship or station. A second officer could also keep a science log. (TNG: "The Offspring" ) Lieutenant commander Data kept a second officer's log, and a science log, while serving as the second officer aboard the USS Enterprise-D. (TNG: "The Defector" , "A Matter of Perspective" , "The Quality of Life" , "Force of Nature" )