It is used to "check back" if opener has major suit support, saying nothing additional about the club suit. It can find 3-5 fits, 4-4 fits (in Standard American) and 5-3 fits (in Acol), and also shows whether opener was maximum or minimum strength for his notrump bid. In five-card major systems, bidding Checkback implies that the responder has five cards in his major, and may have four in the other.  1m – 1M; 1NT – 2  The 2 is "Checkback Stayman". Responses by opener shows the following:  Partnership agreement is required on how to handle the case of holding four of the other major and three of partner's suit. One could agree to bid up the line, or support partner's suit first. If partner cannot support your first suit, he will invite with 2NT or bid game with 3NT and you will then correct to your other suit. In Acol, if the opening bid was a major, opener can rebid his major after a Checkback inquiry to show that it has five cards rather than four and find 5-3 fits. Moreover, 1M – 2m; 2NT – 3 can also be used as Checkback Stayman. It is useful also to include an indication of range, particularly if opener's 2NT rebid is forcing to game and shows a wide points range (15-19). This is achieved by using 3 for minimum hands and 3/3/3NT for maximum hands, or vice versa. After 3, responder can still bid 3/3 to look for a 5-3 fit. New Minor Forcing is an alternative to Checkback Stayman where either 2 or 2 can be used as the checkback bid. It can be used by responder with invitational values or better to find three-card support for his major or to find a 4-4 heart fit if holding five spades and four hearts); it also allows a return to the minor to play.