When we open 1 of a suit and the opponents make a takeout double, a redouble always shows 10+. After our redouble, any subsequent doubles are penalty. If the opener runs prematurely, he is showing a minimum, shapely hand.
2♠ is showing a minimum opener with 6 or more spades.
A new-suit on the 1-level is forcing one round. With a hand such as:
I'd rather get the hearts in at once (with 1♥) instead of redoubling and being subject to preemption. Some 10+ point hands will have the option to go either way (either redouble, or bid at once).
A new-suit on the 2-level is natural and non-forcing. For example:
shows something like:
The hand is limited by the failure to redouble.
This treatment of NF on the 2-level and forcing on the 1-level is by far the most common worldwide (not something special to LC Standard).
Jump shifts are weak [ example: 1♦ (X) 2♥ ].
Jump raises are weak [ example: 1♥ (X) 3♥ ].
2NT is a limit raise over all 1-level openers. [ example: 1♠ (X) 2NT ]. After a major, it shows 3+ trumps; after 1♦ it shows at least 4 trumps and after 1♣ at least 5.
For two OPTIONAL conventions that are for advanced-expert players only, see the next page.
After 1♣ (or 1♦) is doubled, a jump-raise is weak and a jump to 2NT is shown on the main card as an invitational or better raise (over majors, it is called Jordan). When the opening is a minor, it makes sense to invert the meanings of 2NT and the weak jump raise. This is to right-side 3NT. After a weak-jump, 3NT is an unlikely spot. But, after an invitational jump, 3NT is quite likely. The problem with "Standard" is that after the double and the 2NT (minor-suit invitational jump), 3NT will be played from the wrong side. The opener is the one with the likely notrump (stoppers) hand, but the declarer will be the player who might have a singleton. So, using flip-flop, the jump to 2NT shows the preempt and the jump-raise is invitational.
Transfers/BROMAD after double
After 1♥ or 1♠ is doubled, most experts use a form of transfers. The most common (combining effectiveness without too much memory drain) is:
To summarize, starting with 1NT, everything through 2 of our major is a transfer. The 1-under transfer shows a constructive raise. The direct raise shows garbage. Opener will "accept" the transfer any time he would have passed had his partner been showing a weak natural hand in the suit transferred to.
2♦ = "I would have passed a NF 2♦ bid"
Neither of these conventions are part of vanilla LC Standard.
Plus... it's free!