Help understand this code a little better

1

I understand most of it, as I have edited it myself, but still stuck on a couple of things.

mySeconds = 3;
mouseListener = new Object();
function startTimer() {
initial = getTimer()/1000;
}
function doyourstuff() {
_root.onEnterFrame = null;
_root.gotoAndStop(10);
}
_root.onEnterFrame = function() {
elapsedTime = Math.floor(getTimer()/1000-initial);
if (elapsedTime == mySeconds) {
doyourstuff();
}
trace(elapsedTime);
};
mouseListener.onMouseDown = startTimer;
Mouse.addListener(mouseListener);
startTimer();

How come for elapsedTime you cant just say…assuming the following

function startTimer() {
initial = Math.round(getTimer()/1000);
}

_root.onEnterFrame = function() {
elapsedTime = initial
if (elapsedTime == mySeconds) {
doyourstuff();
}
trace(elapsedTime);
};