This is incorrect. The correct rule is the following: Instead of doing the sums, we just consider the blocks of 3 as number together. For example, consider again 12,332,455. Then, the value is 455 — 332 + 12 = 135, which isn't a multiple of 7 so 12,332,455 is not a multiple of 7.
If we consider adedalic examples, then we get 022 — 1 = 21 which is a multiple of 7, so indeed 1022 is a multiple of 7.
This is incorrect. The correct rule is the following: Instead of doing the sums, we just consider the blocks of 3 as number together. For example, consider again 12,332,455. Then, the value is 455 — 332 + 12 = 135, which isn't a multiple of 7 so 12,332,455 is not a multiple of 7.
If we consider adedalic examples, then we get 022 — 1 = 21 which is a multiple of 7, so indeed 1022 is a multiple of 7.