total noob - small number placement in cell

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total noob - small number placement in cell

Postby reber1b » Thu Apr 16, 2020 8:34 pm

Hello everyone. I'm brand new at Sudoku and have been watching "Sudoku Guy" on Youtube. I've been able to follow most of what he has presented until today. In the video I was watching today, I noticed he was placing the small numbers in various positions within a cell, In the early sessions he placed all the small numbers at the top of each cell. But in the session I was watching today, he placed some of the small numbers at the top of the cell, some at the bottom of the cell and some in the center of the cell. I know these placements have some significance but I can't find out what it is. I searched Youtube and then googled the entire internet but never found an answer. Could someone advise me on this?
Thanks in advance, reber1b
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Re: total noob - small number placement in cell

Postby Pupp » Sun Jul 12, 2020 1:17 am

It's pencil marks.

Think about a cell being sub divided into 9 cells.

1 2 3
4 5 6
7 8 9

That's a single cell.

Each spot can only have the number I posted. (That is, only "1" can go into the spot I put a "1", etc.)

The reason is that those are "pencil marks". Tiny temporary numbers that solved use to let them know what candidate numbers could go into the cell. The goal is to try and eliminate all but but one pencil mark number, then that's the the only number that can go into the cell.

When you solve a puzzle, most people just put candidate pencil marks when they roughly have an idea what numbers could go into it, so that you don't have to deal with having too many pencil marks all over the puzzle. Many apps allow you to pre-pencil mark the entire grid, and some problems only start with pencil marks and no other set numbers. Some people always fill in the pencil marks first.

If you use an app, they make using pencil marks much easier, because all apps have that function.

There are puzzles that consists of all, or most of the 81 cells with nothing but pencil marks. Each cell already has some numbers eliminated, so you can puzzle out the solution.
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