Modelling quality is the percentage the MetaTrader 4 strategy tester reports after a backtest, describing how faithfully it reconstructed price movement inside each bar. It rises with the granularity of the input: open-price modelling is fast and close to meaningless, control points is a rough interpolation, and every tick reaches 90% using the platform's own history.
The figure matters because the intrabar path decides whether a stop or a take-profit was hit first. A strategy with tight stops can be reliably profitable at low modelling quality and reliably unprofitable on real ticks, purely as an artefact of the reconstruction. Anything intraday needs genuine tick data, a variable spread rather than a fixed one, and a walk-forward check afterwards. A 90% figure describes the quality of the data, never the quality of the strategy.
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Guide
How Execution Models Work: ECN, STP and Market Maker
Market maker, STP and ECN describe where the other side of a trade comes from — and what each model changes about spreads, requotes and order handling.