GPS, accuracy, and how this thing works

So I've been following samples from the kitchen sink, and adapting the existing code to my needs. Problem is, I think I might have made some mistakes along the way.

I ran my app while I was driving and got somewhere along the lines of 50x the distance I actually traveled.

I am using the following formula to get the distance between to lat/long points:

var getDistance = function (lat1, lat2, lon1, lon2){
    var R = 6371; // km
    var dLat = toRad(lat2-lat1);
    var dLon = toRad(lon2-lon1);
    var lat1 = toRad(lat1);
    var lat2 = toRad(lat2);
 
    var a = Math.sin(dLat/2) * Math.sin(dLat/2) +
            Math.sin(dLon/2) * Math.sin(dLon/2) * Math.cos(lat1) * Math.cos(lat2); 
    var c = 2 * Math.atan2(Math.sqrt(a), Math.sqrt(1-a)); 
    var d = R * c;
 
    return d * 0.621371; // converting to miles
};

I've assumed the return value for that function is in km so I do a conversion towards the end.

The way I call it is as follows:

var updates = 0;
var locationChangedHandler = function(e){
    if (!e.success || e.error){
        // error handling
    }
    if (e.coords != null){
        var longitude = e.coords.longitude;
        var latitude = e.coords.latitude;
        var altitude = e.coords.altitude;
        var heading = e.coords.heading;
        var accuracy = e.coords.accuracy;
        var speed = e.coords.speed;
        var timestamp = e.coords.timestamp;
        var altitudeAccuracy = e.coords.altitudeAccuracy;
 
        addNewCoordinate(latitude,longitude);
        updates ++;
        $.status.text = "UPDATED " + updates;
        $.lblSpeed.text = speed + " mi/h";
    }
};
 
var addNewCoordinate = function(lat, lon){
    var lastDistance = distance;
    distance += getDistance(lastLat, lat, lastLong, lon);
 
    model.distance = Math.round(distance*100)/100; // max 500
    $.lblDistance.text = model.distance + " mi";
    $.lblDistance.text = model.distance;
 
    if (distance > lastDistance){
        var m = Alloy.createModel('Coordinate', {lat: lat, lon: lon, exerciseInstanceID: model.id});
        m.save();
    }
 
    $.lastupdated.text = (new Date()).toString();
    $.lat.text = lat;
    $.lon.text = lon;
};
 
this.startGPSTracking = function(){
 
    Titanium.Geolocation.accuracy = Titanium.Geolocation.ACCURACY_BEST;
    Titanium.Geolocation.preferredProvider = Titanium.Geolocation.PROVIDER_GPS;
    Titanium.Geolocation.purpose = "C7 Tracking";
    Titanium.Geolocation.distanceFilter = 2;  // TODO: make this adaptive
 
    $.status.text = "GPS tracking STARTED";
    // we need to save the model to have an id
    if ((model.id == null)||(model.id === "")||(model.id === 0)){
        exerciseID = 0;
        setEditor.saveCurrentExercise(updateExerciseID);
    }
    else{
        exerciseID = model.id;
    }
    setDistance(model);
 
    Titanium.Geolocation.getCurrentPosition(function(e){
        $.status.text = "First Position Retrieved";
        if (!e.success || e.error) {
            // error handling
        }
        var longitude = e.coords.longitude;
        var latitude = e.coords.latitude;
        var altitude = e.coords.altitude;
 
        lastLat = latitude;
        lastLong = longitude;
 
        addNewCoordinate(latitude, longitude);
    });
    $.status.text = "STARTED";
    Titanium.Geolocation.addEventListener('location',locationChangedHandler);   
};
 
this.stopGPSTracking = function(){
    Titanium.Geolocation.removeEventListener('location', locationChangedHandler);
    $.status.text = "STOPPED";
 
};

The problem is the distance I am getting is about 50x the actual distance. It's probably noteworthy I tested this while driving my car.

I did notice that the speed returned by e.coords.speed returns 28 when I'm traveling at 60 mph. I also noticed that when the car is in full stop, the distance continues incrementing, so there's probably something wrong with how I'm handling the event as well.