After a suit has been agreed upon, a new suit bid at the cheapest level above 3NT, or when the auction is game forcing, is a control-showing cue-bid and is a slam try. It shows a first-round control in the bid suit: either an ace or a void. If the suit is cue-bid again, it shows second-round control: a king, a singleton or a void. Control showing bids are a key aspect of slow approach.
Controls are bid from the lowest available suit up, while bypassing a suit denies control in that suit. An example:
- agreeing the suit
- spade control, slam try
- diamond control, denies club control
- cuebidding the second time shows a second-round control
- an attempt to sign off
Once cuebidding has started, the auction can be stopped only at the agreed trump suit:
- A non-agreed suit bid is a control-showing cue-bid
- A trump suit bid is an attempt to sign off, showing either no more controls or no further interest. Partner can continue to cue-bid to insist the slam try.
- 4NT is Blackwood.
- A non-jump 5NT asks for the top honours.
- Jumping to 5NT is grand slam force.