OHLC vs tick data

Two data fidelity tiers. An OHLC bar gives four prices per period and hides the path between them, so a backtester cannot know whether the high or low came first, which matters when a stop and target sit inside the same bar. Tick data records every quote but, in some platforms’ ‘every tick’ modes, is largely reconstructed synthetically and can order the high and low wrong.

First used in Lesson 2.4 · Event-driven backtesting with honest costs — the lesson that makes this term real.