The consensus rule that periodically recalibrates mining difficulty so average block time stays near the target despite hash rate changes.
A Difficulty Adjustment Algorithm (DAA) updates the proof-of-work target to keep blocks arriving at a predictable cadence (e.g., ~10 minutes for BTC, ~10 minutes for BCH). By raising difficulty when hash rate rises and lowering it when hash rate falls, DAAs stabilize issuance and network timing.
Bitcoin recalculates difficulty every 2016 blocks (~2 weeks). If blocks arrived too fast in the last period, the target becomes harder; if too slow, easier, bounded by a 4× change limit.
Different chains use different DAAs. Some adjust per period (e.g., BTC 2016-block retarget), others adjust every block with smoothing filters (e.g., BCH ASERT), and some use hybrid schemes.
Bitcoin Cash adopted ASERT in 2020 to adjust difficulty every block using an exponentially weighted target, improving responsiveness and reducing oscillations from miner switching.
Poorly tuned DAAs can cause unstable block times, fee spikes, and issuance distortions. They can also be manipulated with timestamp games or oscillation attacks if not designed carefully.
A slow-reacting DAA can lead to long block droughts after a hash rate exodus; a hyper-reactive DAA can amplify oscillations as miners chase short-term profitability across chains.
All terms and definitions may update as the Cryptionary improves.