Hands Off the Bidding Box!
The Bidding Box is a great invention: it makes it easy to remember the auction and avoids all accusations of verbal inflection that might carry Unauthorised information — but it has produced another way to convey Unauthorised Information:
DO NOT FIDDLE WITH THE BIDS IN YOUR BOX!
Decide which call you wish to make and reach for the Box only after making your decision. The only time you should touch the Box is to grasp the call you have decided to make. Once you take hold of a bidding card it is too late to change your mind.
This does not mean that once a call has been removed from the Box it cannot be changed. You may not change your mind about a call. You must make the call you intended to make.
If you make a mechanical error – you inadvertently pull the wrong card, or another card has stuck to the one you intended to make – you should change to the bid you intended to make as soon as you notice your error. Put the Bidding Cards back and try again. Do this even if it is partner's alert that draws your attention to the mistake.
You should change a mechanical error even if the next player has also made a call. Their call is retracted. They can do whatever they like without penalty and any information gained by his partner is Authorised.
If you do not notice your error until after partner has called it is too late. You are stuck with your mechanical error and must muddle through.
The Laws of Contract Bridge do not yet cover Bidding Boxes. There are special Regulations about the use of the Bidding Box: they can be found on this site.