Cappelletti convention

Cappelletti (also called Hamilton and Pottage) is one of many defensive bridge bidding conventions used in the card game contract bridge to compete or interfere in the auction when an opponent has opened one notrump (1NT). Usually attributed to Michael Cappelletti and his longtime partner Edwin Lewis, origin of the concept is also claimed by Fred Hamilton, John Pottage and Gerald Helms. Cappelletti can show a variety of one- and two-suited hands while retaining the penalty double for stronger hands.
Application.
Cappelletti is particularly recommended for use against a weak 1NT opening (12-14 HCP) but can also be used against stronger 1NT openings (15-17 HCP). Cappelletti can be employed in either the direct or balancing seat.
Double.
When holding 15 or more high card points (HCP), a Double is for penalties.
Overcalls.
With 9-14 HCP, other overcalls are artificial bids promising either a one-suited or two-suited holding. Importance is given to the state of vulnerability and the location of the values, which should be concentrated in the suit or suits held. 
Over the 1NT opening, the over-calling opponent (known as 'Intervener') makes one of the following artificial bids to indicate a one-suited or a two-suited hand:
All artificial bids must be alerted.
Reverse Cappelletti or Multi-Landy.
This variant reverses the 2 and 2 bids above, so that for hands with both majors it is similar to the Multi-Landy convention.
Extending the bidding towards game.
With a strong hand of his own, (13+ HCP) Advancer may think that the defensive partnership could have the possibility of a game call themselves.
To explore this possibility, any bid by Advancer beyond the natural conclusion of the Intervener calls described above, is invitational to game.&lt;br&gt;Such a bid shows most importantly the High Card Points range in Advancer's holding (which should be 13+ HCP — at weakest, Intervener has promised only 9 HCPs, and since bidding is now advancing to the 3-level, 13 HCP in advancer's hand guarantees a minimum joint holding of 22 HCP for the partnership).
The most common and most useful circumstance for this, is when the defender's own game call is likely to be 3NT. Look at the following scenarios:
So if Advancer's holding is 14+ HCP and with stops in the other suits, (bearing in mind that partner might have shortage in at least one of them so those stops need to be dependable), Advancer might extend the bidding to 2NT asking Intervener 'are you top or bottom of your points range partner?'.
With only 9-10 HCP, Intervener either passes, or if his own suit is likely to perform better, signs-off by re-bidding his own suit.
But with 11+ HCP, thus promising a partnership holding of at least 25 HCPs, Intervener advances to a game call of 3NT.
Finally if Advancer has shortage in the Capelletti suit then 3NT is passed, but with 3+ card support for partner's Cappelletti MAJOR suit, then sign-off by correcting to a game call in the major suit.
(With the opposition opening 1NT it is unlikely you would want to go beyond 3NT if the Cappelletti suit is a minor).
So if Advancer is holding 14+ HCP and three cards in hearts, Advancer should extend the bidding to 3 asking Intervener 'are you top or bottom of your points range partner?'.
With only 9-10 HCP Intervener now assesses the his shortage points using, possibly, the method of 'Losing Trick Count' and thus decides whether to pass 3 or sign-off with a game call of 4.
Of course with 11+ HCP Intervener doesn't need to think before signing-off with a game call of 4.
So with Advancer's holding of 14+ HCP but only two cards in hearts (happens to be merely two small values for example) Advancer bids 2NT inviting Intervener to bid his minor. So the bidding sequence has now been 2-2NT-3.
Advancer now has to assess what the joint holding is; Partner likely has stopping values in Hearts, but anyway partner's length assures the Heart suit is safe. Provided that Advancer has stopping values in the other three suits in his own holding (bearing in mind that partner may not have stopping values in Diamonds, merely 4-card length), the only question for Advancer is whether or not the HCP holding for the partnership is strong enough for 3NT.
Unless Advancer has 16 HCP minimum, this becomes a judgement decision (can we afford the risk of 1-off? do I hold 14 HCP? 15 HCP or better?
Given that Partner's range could be as little as 9 or 10, if I hold 14 HCP then the balance of our holding is more likely than not to equal 25+ HCP, and finally, with our holding being this high, we know where most all outstanding cards are i.e. in Opener's hand, so does that possibly help us to place the lead into Opener's hand leading towards a tenace perhaps in ours, or to finesse?
Much to consider but so many likely situations that support a 3NT call for our partnership.