1. Left edge
Start with the leftmost window.
2d x 2d (mastery)
4 visual steps / 2x2 window scan
2. Cross window
Add both crossing products.
3. Right edge
Finish the ones product.
4. Settle strip
Keep 1s; extra carry moves left.
Practice Level 10
A few quick rounds make the train automatic; each raw window keeps one digit.
Start Level