Once a day (at 00:00:00 UTC) every provider makes a copy of the ledger and calculates its root hash. This hash lets to compare all existing qubics using a 256-bit number, if there is a difference even in a small piece of two copies of the ledger then these hashes will be different. Every provider asks the others for the root hash and compares its hash to the hash of the quorum, and if there are any differences it requests data necessary to build identical ledger. If a provider is bootstrapped then it downloads entire set of qubics.