I use my vacuum gauge as my primary instrument and then confirm its benefit with the
MPGuino. Keep the vacuum as far away from 0 as you can (within reason, you'll see) and then see what the
MPGuino is telling you. You do have to compromise on hills and during accelerations but you get used to the instantaneous info. It is a great way to gauge where your throttle position needs to be once you are used to it and the drive you do most often. Another trick is when you are driving at constant speed and power like on a long stretch of road. Lift you foot just ever so slightly and see the response on the vacuum gauge. You end up at the same speed but more vacuum and less fuel used.
I love mine!