How to Spot Curve Fitting

The five signs

Curve fitting is a rule shaped to the bars it was tested on, and it gives itself away by five signs. Odd numbers: the best hours on the euro for 17 to 21 August 2026 were buy at 01:00 and sell at 19:00, which nobody would have chosen in advance. Too good: 122.8 pips in a week where the plain 10:00 to 18:00 rule made 39.0, where a pip is the fourth decimal place of the price. One day: 89.4 of the 122.8 came on the Wednesday. Everyone wins: 243 of the 276 possible hour-pairs made money that week, so the week was the edge, not the hours. And it falls apart: the same hours on the following week lost 79.0. All five were visible before the next week arrived.

A key cut to one lock

Picture a key cut to one lock. Every notch on it matches one pin in one door, and it turns that lock perfectly; it will not turn the door next to it, because the next door's pins are different, and the more exactly the key fits this door, the less it opens any other. A fitted rule is that key: its hours and its numbers were cut to the pins of one week's bars, and the perfection of the fit, which looks like the best thing about the rule, is the evidence against it.

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