Real technique, real rules, and your left-side evidence is exactly why it exists.
"Evenly hot" is a myth home ovens tell on their packaging - heating elements, door gaps and airflow give every oven its personal hot spots. Yours clearly lives on the left. Rotation evens out what the oven won't.
The rule: rotate at about 70% of the bake time. Late enough that the structure has set - cakes and delicate rises knocked around early can deflate - but early enough that the remaining time evens the colour. For your cookies: 12-minute bake, spin at minute 8, front to back and the fast side to the slow side.
What NOT to rotate: anything in its fragile rising phase (soufflés never, cakes not before the centre sets), and don't hold the door open while you contemplate - fast hands, heat stays in.
One tray, one spin, at 70%. Both sides of your cookie batch finally matching 🍪
