Increasing Counters

HTML

<h3>Left</h3>
<span id="left"></span>

<h3>Mid</h3>
<span id="mid"></span>

JavaScript

function numberWithCommas(x) {
    return x.toString().replace(/\B(?=(\d{3})+(?!\d))/g, ",");
}

function timeSince() {
    var prevTime = new Date(2015,8,8,0,0);
	var thisTime = new Date();
	return (thisTime.getTime() - prevTime.getTime()) / 100;
}

function parcelCount() {
    var secDiff = timeSince();

	var leftNum = document.getElementById("left");
	var midNum = document.getElementById("mid");
    var leftNumCount = Math.round(((76/60) * secDiff) + 40093794);
    var midNumCount = Math.round(((43/60) * secDiff) + 22874098);
    
    leftNum.innerHTML = numberWithCommas(leftNumCount);
    midNum.innerHTML = numberWithCommas(midNumCount);
}
parcelCount();
setInterval(parcelCount, 10);