I need to change the battery on my Sigma 1106 bike computer and I have not been able to detach the main unit from its 'station'. (I've removed it before...but I can't recall just how it comes off.)

The owner's manual is mainly diagrams (as well as brief instructions in several languages) but does not seem to address actual removal of the unit. I believe it twists off, but gently twisting in either direction has not been successful. Am I missing a step? There doesn't appear to be a 'release' tab (like my other bike's Cateye computer.).

Would appreciate any suggestions; thanks in advance for your help!