I find that the Hornady anvil Base has a tendency to obscure my readings. That being said, this is why I say this, and I own 4 of these. In new brass you want see this as much, but in cases with 10 to 30 firings on them. "Lapua 6.5CM, SRP, annealed after every shot." It's very obvious, The base is no longer squared or it has snags from the extractor and ejector. When you place the bullet case on the perfectly flat anvil it will show a different reading verses not using it. That's in a bolt rifle,,,. Now if you really want to see some thing that will have you scratching your head. Use it on some 223/5.56 brass fired out of a AR-15 or 308 out of a AR-10, after one firing.
I loved the concept of the anvil, but, I'm doing just great with out them. Mixed readings when your OCD weighs heavy on the mind, like chasing lands. LOL