Support and resistance (S/R) are price levels where a pair historically reversed direction. Support is a floor, price bounced up from it before. Resistance is a ceiling, price turned down from it before. Signals near these levels have higher probability than signals in "empty" price space.
Institutional traders place large orders at round numbers, 52-week highs, and prior reversal points. When price reaches these levels, the cluster of orders causes a visible reaction. By tracking where price has reversed in the past, the system identifies where orders are likely clustered now.
The Historical S/R rule checks whether the current price is within a threshold of the 90-day high or 90-day low. Near the 90-day high, the system adds a SELL bias (resistance). Near the 90-day low, it adds a BUY bias (support). This is a data-driven, automated S/R approach.
The Round Level rule is a companion to S/R. When price is within 15 pips of a major round number (1.0900, 1.1000, 148.00, 2400.00 for gold), institutions are likely placing limit orders there. Round levels act as S/R even without prior price history at that exact level.