Step from a fixed alarm line, which rings every busy evening, to residuals (actual minus expected), which catch the real 4 a.m. spike and 8 p.m. drop.
The alarm rings for any hour over 150 orders. It rang 7 times, all between 6 and 10 p.m., the usual evening rush. It missed day 2's 90 orders at 4 a.m. and the drop to 20 at 8 p.m.
