Iphone – MKMapView: How to set the region span based on the Accuracy

Im implementing a map application on iPhone. I want the map to zoom in on the user's current location.
I'd like to zoom closer based on the accuracy (emulating how the Maps app works).

Im implementing this method:

    - (void)locationManager:(CLLocationManager *)manager 
didUpdateToLocation:(CLLocation *)newLocation 
fromLocation:(CLLocation *)oldLocation {

The problem I face is that CLLocation provides me the accuracy with the properties horizontalAccuracy and verticalAccuracy, that in the end means meters. However, to center the map I using this:

MKCoordinateRegion region;
MKCoordinateSpan span;
region.center = newLocation.coordinate; 
span.latitudeDelta=.005;  //THIS IS HARDCODED
span.longitudeDelta=.005; //THIS IS HARDCODED   
region.span = span;

[mapView setRegion:region animated:YES];

Im looking for a way to calculate the latitudeDelta (represented in degrees) based on the horizontalAccuracy (represented in meters).

It doesn't need to be a exact conversion (Im not looking forward a conversion formula, that will require quite some calculation, including the current location), just some aprox values.

Any ideas?

Thanks.
Gonso