If seeing all of the possible numbers in the cells looks overwhelming, only notate the squares that have 2 or 3 potential numbers instead.
Once you fill in the number, check the row, column, and box that the cell was in and erase any other instances of that number. Be on the lookout for “hidden singles” as well. You can fill in a number if it isn’t written down anywhere else in the same row, column, or box, even if there are other candidates in that cell.
“Hidden pairs” are similar but a little trickier to find. The 2 cells are the only places where the numbers can be placed, but the cells may have notation for other potential candidates.
Example: If the cells contain 1 & 5, 1 & 8, and 5 & 8, the values 1, 5, and 8 have to go into those cells and can’t be written in other cells in the same row, column, or box.
Example: If A1 and C1 are the only cells in a box with 4 as a potential candidate, you can erase all other 4s from the first column. Example: If D4, D5, and D6 are the only spots in the middle box that can contain 8, no other cells in the D row can have 8. You won’t know which cell the number goes into quite yet, but pointing pairs and triples should help narrow down your options for other cells.
Mark the square you started in so you can retrace your steps.
Example: If a 2 could only be in the 1st and 7th columns in rows E and G, then you can erase 2 as a potential candidate from all other cells in those rows.
Example: A2 is the pivot with 3 & 8. The pincers are I2 with 4 & 3 and A6 with 4 & 8. The intersection between I2 and A6 is I6 with 4 & 5. Since 4 is in both of the pincer cells, you can eliminate it as an option from I6.
Forming an angle means that 2 of the cells are in the same row or column, but the third cell can be positioned anywhere that shares a row, column, or box with one of the others. Example: B1 could be 4 or 9, B5 could be 1 or 9, and D1 could be 1 or 4. The cell D5 couldn’t be 1 since it would make filling in B1 impossible. That means you can eliminate 1 as a candidate from D5.
Example: The only cells in rows B, E, and F that can contain 1 are B1, B7, E5, E7, F1, and F5. Since you can draw a closed loop connecting these cells, you can erase 1 from any other cells in the same columns as these cells.
Example: 2 & 3 are the only potential candidates in D4, D5, and I4. I5 has 1, 2, 3, & 8 as potential candidates. With a unique rectangle, you can eliminate 2 & 3 as options from I5.
