[iamrosen]

Would someone please give a concrete example of exactly how a robot uses the 8421 system as a cue bid in a suit with more information than A=8, K=4, etc.?

[barmar]

Welcome to the forums, iamrosen. I've moved your post because it's about BBO, not about bridge in general.

8421 points are how GIB keeps track of which honors have been cue bid. It always shows aces first, then kings on the next round. So the first cue of a suit bid shows 8+ 8421 points. And if it bypasses a suit, it means it doesn't have the ace, so it says that it has 7- 8421 points. If it cue bids the same suit again, it's now showing both the ace and king, so it has 12+ 8421 points.

If you're familiar with binary arithmetic, you'll notice that these are all powers of 2, and 8421 is a binary bit mask corresponding to the 4 top honors. GIB uses this in non-cue-bidding contexts to describe a suit's honor texture. For instance, sometimes GIB will jump to 5 of the trump suit. This usually means that it has a good hand that it thinks is suitable for slam, except that its trumps are poor, and it will describe it as something like 3- 8421 points in trumps. It wants you to bid 6 if you have good trumps.