Normal sudoku rules apply. In addition, each unique letter of "FOURTH OF JULY" represents a unique digit from 1-9. The two-letter sandwich clue represents a two-digit number where the first letter is the tens digit and the second letter is the units digit. Along thermometers, digits must increase from the bulb end. Clues outside the grid give the sum of the cells "sandwiched" between the 1 and 9 in the relevant row/column.