Repainting indicators and how to spot them

[Shadow Trader]

A repainting indicator changes its past values as new data arrives. On a finished chart, it looks perfect, with signals at every turning point. In real time, the signals shift or disappear.

Classic examples include zigzag lines, some fractal indicators, certain trend-line detectors, and many "signal" indicators sold online with spectacular screenshots. The perfection comes from the fact that the chart shows the final, rewritten history.

How to spot one: watch the indicator in real time. Record where signals appear and compare them with the finished chart an hour later. If arrows move or vanish, the indicator repaints. Another check is to load the indicator into a strategy tester in visual mode and watch it bar by bar.

Not all repainting is deceptive. Some indicators naturally recompute as bars develop, and the issue is whether the strategy treats the unconfirmed values as final.

Using only signals confirmed at bar close, and testing on forward data, protects against false confidence. Any indicator whose seller refuses to show real-time behaviour deserves suspicion.

A short checklist for any new indicator: does the seller show real-time recordings, not just still images? Does the documentation mention repainting? Does the indicator use future bars in its calculation? Can its values at a past bar be reproduced from data available at that time? Four questions, and a failure on any one is a warning.

Has a repainting indicator ever fooled a test, and how was it caught?