I think you have issue with your conversion formula because 12.6 Brix is about 1048.
What formula are you using?
Thirsty_Monk, that could be. I tried using a chart on another forum but it was further off than the following formula. I searched the net until I found the following formula which I have been using:
SG = 1.000898 + 0.003859118*B + 0.00001370735*B*B + 0.00000003742517*B*B*B
B = measured refractivity in Brix
SG = calculated specific gravity at 15 C (59F)
any further help would be greatly appreciated.. thank you