So I think that it's because with a BT they can see the actual amount. I just said the 16th because if it halves every 35 hours then your HCG will be at 3.94 (which isn't enough to show up on a FRER) on the 16th. But that depends on when you did your shots and all the other things I mentioned before. It's hard to calculate this stuff when you don't know what your body will do!
Aww. Hang in there! I do hope you're wrong this time. lol