I'm also using wein cells, although with 1.5v cell B+W films were correct. But i'm usually using Velvia. Exposure seems to be slightly different with the wein cell.
By the way, do not rewind anti-clockwise. I've done that today, then opened the film door. I'm still angry, I have lost a Velvia roll. The rewind knob then fell apart. It's supposed to be done clock-wise...
😉