When the 30-day average falls below the 60-day, hash rate is declining and the indicator is said to signal capitulation. The crossover back above is treated as recovery, and some versions add a price-momentum confirmation before flagging a buy.
It is a moving-average crossover on a noisy series, with all the usual properties: it lags, it whipsaws, and its historical record rests on very few completed cycles. Hash rate is also estimated from block intervals rather than measured, so short-window readings are statistically shaky.
Its main honest use is descriptive: it marks periods when mining economics were under stress, which is genuinely informative about the industry. Treating the crossover as a trade signal is fitting a rule to a handful of past instances, and this is not a recommendation to do so.
Related: miner-capitulation, hash-rate, mining-difficulty, moving-average