# bits The difficulty target in compact (`nBits`) encoding — the threshold the block’s hash must meet or fall below for the proof-of-work to be valid. ``` var bits: UInt32 { get } ``` ## Discussion Decodes per Bitcoin Core’s [`arith_uint256::SetCompact`](https://github.com/bitcoin/bitcoin/blob/master/src/arith_uint256.cpp): top byte = exponent, low 23 bits = mantissa; the full 256-bit target is `mantissa << 8*(exponent-3)`.