I need to create a UIToolbar that has two UIBarButtonItems. The 1st button must be centered and the 2nd item must be right aligned.

I understand and use Flexible spacing and it works great when I need to balance buttons across the UIToolbar, but with only two buttons, I can't seem to perfectly center the middle button. I've even initialized the view.toolbarItems array with

NSArray *items = [[NSArray alloc] initWithObjects:fixed, flex, center_button, flex, right_button, nil];

and set fixed.width = right_button.width ... but still, the center_button is never perfectly centered.