## total noob - small number placement in cell

Everything about Sudoku that doesn't fit in one of the other sections

### total noob - small number placement in cell

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?
reber1b

Posts: 1
Joined: 16 April 2020

### Re: total noob - small number placement in cell

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.