I am not sure that classical 1♦ Precision opening is 4+♦ (doubt it!), but certainly is 11-15 HCP. From C.C. Wei and Berkowitz classic books on Precision, 1♦ opening is 2+♦ and 11-15 HCP. Below is what I play with my regular precision partner on 1♦ opening: 1♦ ...1♥!/♠!: 6+ HCP, can have just 3 cards (although Opener shld assume 4+), can have the other major, F1R ......1♠: 11-15 HCP, 4♠, unbalanced ......1NT: 11-12 HCP, balanced, can have 4♠ & 3♥ investigated through checkback stayman ......2♣: 11-15 HCP, unbalanced, can have more ♣ than ♦ ......2♦: 11-13 HCP, 5+♦ ......2♥: 11-15 DH, 4+♥ ......2♠: 16+ DH, mini-splinter to ♥ ......2NT: 14-15 HCP, 6 card solid ♦ suit ......3♣: 14-15 HCP, at least 5/5 in the minors ......3♦: 14-15 HCP, not so solid ♦ suit :) ......3♥: 16+ DH, 4+ ♥ ......3NT: 14-15 HCP, 7 card solid ♦ suit ...1NT: 8-10 HCP, usually balanced but can have long ♣s if no tolerance to ♦s, denies 4+ major, NF ...2♣: 11+ HCP, 4+ ♣s, can have 4+ major, F1R ...2♦: 11+ HCP, 5+ ♦s, denies 4+ major, F1R ...2♥/♠: 2-5 HCP, 6+ major good suit, no outside values, to play ...2NT: 11-12 HCP, balanced, denies 4+ major, NF ...3♣!: 8-10 HCP, 5+ ♦s, denies 4+ major, F1R ...3♦: 0-7 HCP, 5+ ♦s, preemptive ...3♥/♠/4♣ are splinters to ♦ ...3NT: 13-17 HCP, balanced, to play ...4♦: preemptive ...4♥/♠: to play