I have a Sigma BC 1600 computer. The button you need to press to enter and leave the setup mode is a tiny little button you press with a pen or similar underneath the unit near the mount. There's 2 buttons. The one on the left changes from wheel size 1 to wheel size 2 and the one on the right is the one to enter and leave the setup mode.

Ciocc77, I think that you are giving instructions for a Sigma BC 1106 which I have as well. Thats a very frustrating computer to setup.

Regards, Anthony