CoinMetrics uses the distribution of valid pseudorandom nonce values to identify the presence and evolution of ASIC miners across a variety of Proof of Work metrics. A nonce value is found by hashing a block header using a cryptographic function (such as SHA-256); valid blocks have a nonce value lower than a predetermined target. Since any nonce can produce a winning hash and confirm a block, it is expected that nonces be distributed randomly. In a variety of networks, most clearly Monero, nonce distributions are non-uniform and frequently change around the time that ASICs are deployed.