How Bitcoin Unlimited works

Please review these examples of emergence first:
http://www.pbs.org/wgbh/nova/sciencenow/3410/03-ever-nf.html

Assume a BU majority network.
Consensus occurs on the max block size over the whole Bitcoin network from low-level rules used by thousands of individual nodes. There is no voting.

With Core and XT everyone needs the same maximum for block size. BU is different in that only the whole network possesses the attribute of a dynamic block limit, while each individual node has an approximation, or even a limit which is a lot smaller or larger. It doesn't matter, except that nodes with a too-small limit will frequently have the latest blocks "on probation" waiting for them to reach an acceptance depth. A node which sees a block which is excessive (over its limit) will not relay or process it until it is buried under enough confirmations. BU nodes always track the chain tip with the most PoW.

A miner producing a block larger than emergent network consensus gets its block orphaned. As individual node owners update their settings after upgrading or getting new hardware, bandwidth etc, then the network consensus slowly changes, usually upwards although the exact value at any one time is an irrational number and unknowable.

Individual node settings:

• Excessive block limit (default 16MB)
• Acceptance depth, i.e. confirmations (default 4)