Jacoby 2NT + SST

SST theory

SST (Short Suit Total) = number of cards in 2 shortest suits of both partners.  

When having 9(8) card fit, the expected number of tricks is 13-SST (providing the partnership holds 20 HCP). Each additional 3 HCP, provide another trick

1♥ - 2♠    ➲

1♠ - 2NT    ➲