A responsive double is used after partner makes a takeout double or simple bid. It occurs when:

• LHO opens a suit;

• Partner makes a takeout double  or simple bid;

• RHO raises at most 3♠.

A double in this situation shows at least 4-4 shape in (HCP in total):

• the major suits if the opponents bid a minor, 18+HCP at the 2-level, 20+HCP at the 3-level;

• the minor suits if the opponents bid a major, 20+HCP at the 2-level, 22+HCP at the 3-level;

• denying the partner suit support.

Further the calculated bid.