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Indicator classroom — honest guides to common trading signals

Every indicator in our rule engine, explained honestly: what it measures, how it's computed, and the specific way it fools people. Each page links to a browser playground on real data.

Prior high / low breakout (and the look-ahead trap)
Rolling high/low breakouts look great in backtests until you notice the current bar is inside its own level. The shift(1) detail that separates a real signal from self-deception.
RSI — what 30/70 actually tells you
RSI compresses recent up-moves vs down-moves into 0-100. Useful in ranges, dangerous in trends: in a strong move it pins at the extreme while you keep catching knives.
Moving averages & crosses — lag is the price of smoothness
SMA weights all N bars equally; EMA front-loads recent bars. Crosses are robust trend filters that are late by construction — the question is whether the trend pays for the lag.
Bollinger Bands — reversion tool, trend victim
Bands at mean ± 2 standard deviations adapt to volatility automatically. Touch-and-revert works in ranges; in trends the band "walks" and every touch is another loss.
ATR & ATR% — measuring volatility without fooling yourself
Average True Range says how much an asset actually moves per bar. Good for stops and squeeze detection; the trap is that any fixed threshold is arbitrary across assets and timeframes.
Volume ratio — "is anyone actually here?"
vol_ratio compares current volume to its rolling average. It confirms breakouts and filters dead hours — and has one classic silent-failure parameter everyone hits once.
Rolling z-score — thresholds that survive regime change (mostly)
A rolling z-score asks "how unusual is the current value vs its own recent history" instead of hardcoding a magic number. It fixes drifting thresholds — but it is not trend-immune, and we can prove it.
Retail long/short ratio — crowding as a contrarian signal
The ratio of retail accounts long vs short. The crowding-reversal thesis shorts euphoric crowds. The catch: its "normal range" drifts with regime, so absolute thresholds silently die.

Research and education. Not investment advice. No indicator makes money by itself — our own arenas' honest records (losses included) are on the scoreboard.