One more picture. I have many rulers and squares. I was going to use the wider aluminum ruler to take the above pictures, because it is brighter than the ruler from the combination square, and shows up in the pictures better. When I did, I noticed that it gave me a different rail height. I was scratching my head, until I checked that ruler agains my Starrett brand ruler (Starrett is the top brand in machinist tools). As you can see, the aluminum ruler is off quite a bit. Just food for though, that when trying to get very accurate measurements, you can't blindly trust your measuring tools