z .: move the current line to the center (in German: zentrum) of the viewport.
z t: move the current line to the top of the view port.
z b: move the current line to the bottom of the view port.
ctrl y: move the viewport up one line. Yore (long ago), or, Yesterday.
ctrl e: move the viewport down one line. Efter means after in Swedish.
ctrl b: move the viewport up/backward half/one page. Backward has more characters than up, so the movement takes further.
ctrl f: move the view port down/forward half/one page. Forward has more character than down, so the movement takes further.