For a few months I've been working on a small algorithmic trading project on the side — partly to learn ML on real (and brutally noisy) data, partly because finance is one of the places where measurement and model meet in interesting ways. The setup is unremarkable: a universe of 16 sector and broad-market ETFs (SPY, QQQ, DIA, the XL- sector series, IWM, IYY), per-ticker models that produce daily forecasts, and a rules-based execution layer with stop-losses on top.