Normal sudoku rules apply. Each digit in column 1 indicates the position of the 1 in its row. (eg if R5C1 is a 6, then R5C6 is a 1 as the 1 must appear in the 6th position). Column 5 operates the same way for the digit 5; and column 9 for the digit 9. Each digit in row 1 indicates the position of the 1 in its column. (eg if R1C5 is a 6, then R6C5 is a 1). Row 5 operates the same way for the digit 5; and row 9 for the digit 9. On thermometers, digits must increase from the bulb end. Along the marked diagonal, digits must not repeat.