What does the "block number" in the iota wallet represent?

Question

My iota wallet displays something that I would assume to be a block number in the lower left corner: 291911

But being aware of the Tangle structure, I know there are no blocks in iota. What does this number represent? Bundles?

Answer 1

The two numbers are the

• the latest solid subtangle milestone index
  The "latest solidsubtangle milstone" is used for sending transactions. For a milestone to become solid your local node (or whatever node your lightwallet is connected to) must basically approve the subtangle of coordinator-approved transactions, and have a consistent view of all referenced transactions.

and

• the latest milestone index
  A milestone is a special transaction issued by a special node called Coordinator. The Coordinator is run by Iota Foundation, its main purpose is to protect the network until it grows strong enough to sustain against a large scale attack. Milestones set the general direction for the tangle growth and do some kind of checkpointing. Transactions (in)directly referenced by milestones are considered as confirmed.

The Coordinator also posts the milestone indexes and some extra information into the #botbox channel in the IOTA Slack:

More info about milestones:

• IOTA Node Tutorial by necropaz
• getNodeInfo documentation
• tangleblog