Term
 row  a single row
 column  a single column
 square  a single cell
 3Row  a group of 3 rows; rows 13, 46, or 79
 3Column  a group of 3 columns; columns 13, 46, or 79

9Square  a square of 9 cells with a bold border
 Pairacross
 Find 2 rows in a 3Row with a shared value. Check the 3rd row of the 3Row in all its 3Squares to see if you can find a square for the 3rd instance of the shared value.
 Repeat for all 3Row and 3Column.
 2 squares remain
 In a 3Square, when only two empty squares remain, ask yourself what 2 values remain. See if only one legit mapping of those values to empty squares exists.
 Ditto for a row with only two squares remaining.
 Ditto for a column with only two squares remaining.