The exact name used to describe this method will not always be identical to either of those shown above.
In this method the trial bid will promise any one of ace, king, singleton or void (i.e. a first- or a second-round control).
On a bad day you will could in theory find yourself in a slam with two aces missing but in practice this is not a possibility about which you should concern yourself unduly. With the majority of the points in the pack held between the two hands, your bid of a king will frequently find the ace in partner’s hand after which all becomes clear. Some experts combine this bid with a high-level method which determines the exact nature of the stop held.
More often you will save space in the bidding and therefore exchange more information at a lower level.
The method is particularly illuminating when a suit is bypassed at a lowish level and and partner is able to stop quickly knowing of the absence of both the ace and king of a suit.
A K Q 8
Q 8 4
K Q 7 5
2NT agrees spades and is forcing to 3♠ or higher.
If partner is missing the two top clubs he will know not to bid beyond 4♠.
A slight variation of the method shows first- or second-round controls at and below the four-level, but promises a first-round control when used at the five-level or higher.
A further refinement, as in the case of first-round controls, is not to bid a shortage in a suit which partner is known to hold - he needs to know that your honour will serve to make the side-suit solid.
This method is commonplace on the tournament circuit at the present time.
As such I must commend it to you, but use it with a degree of care.
As with ‘first-round controls’ it will usually be used as a slam-try following major suit agreement at the three-level.
If you are new to slam-try trial bids and cue-bidding then there is something to be said for adopting the method of ‘first-round controls’ in the first instance before progressing onto the present style.
You should also consider adopting the ‘how good are you?’ style in at least one specific circumstance alongside this approach.
A method in common expert use.
Use it with care, and use it alongside other styles where appropriate, and it will serve you well.