var dragging = false, startpoint, endpoint, midpoint = $("#center").position();
midpoint = {x:midpoint.left - 2, y:midpoint.top-2};

$("#stage").mousedown(function(e){
    dragging = true;
    startpoint = {x:e.offsetX, y:e.offsetY};
});

$("#stage").mouseup(function(e){
    dragging = false;
});

$("#stage").mousemove(function(e){
    if (dragging){
        var angle = 0, sp = startpoint, mp = midpoint;
        var p = {x:e.offsetX, y:e.offsetY};
        var sAngle = Math.atan2((sp.y-mp.y),(sp.x - mp.x));
        var pAngle = Math.atan2((p.y-mp.y),(p.x - mp.x));

        angle = (pAngle - sAngle) * 180/Math.PI;

        $("#display").text(angle);
        $('#rotateme').css({ rotate: '+=' + angle });

        startpoint = {x:p.x, y:p.y};
    }
});​

if (x2 < x1)
    dist = -dist;