1. Fill thousands
Thousands window: 6 + 8 = 14. Hold raw 14; carry settles later.
5 visual steps / large answer-window addition
Thousands window: 6 + 8 = 14. Hold raw 14; carry settles later.
Hundreds window: 2 + 4 = 6. Hold 6; wait for carry from the next window.
Tens window: 9 + 6 = 15. Hold raw 15; settle carry later.
Ones window: 7 + 8 = 15. Hold raw 15; settle carry later.
Settle raw 14 | 6 | 15 | 15 into 14765; keep ones and move carry left.
A few quick rounds make digit release automatic; carry is the only thing to keep.
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