I found this re racket stiffness from TW on another site:
Tennis Warehouse says:
March 29, 2012 at 11:18 am
Please rest assured that our RDC Machine (“racquet bending machine”) is accurate as are our specs. I want to clarify the specs on our website. What we post (weight, swingweight, flex, balance) are all STRUNG specs. The specs that manufacturer’s list on their racquets and what most websites post are for UNSTRUNG specs. When a racquet is strung, the stiffness (RA) drops 4-6 points, the weight goes up about .6 ounces, swingweight goes up and the racquet becomes more head heavy.
You’ll never hit a tennis racquet without strings, so why have the unstrung specs? That’s how we approach it.
Again, please rest assured that our specs and our machine are accurate. If you have any other questions or concerns, please email us.
Thank you,
Jason, TW