Using the numbers in the segments of the lower two circles, the numbers in the upper left circle equal the sum of the numbers in corresponding segments of the lower 2 circles, the numbers in the upper central circle equal the difference between numbers in corresponding segments of the lower 2 circles, and the numbers in the upper right circle equal the product of the numbers in corresponding segments of the lower 2 circles.
Working from left to right and reading each pair of numbers as a 2 digit value, these values represent the sequence of multiples of 7, starting at 49 and finishing on 70.
Work through the diagram in columns. The value in the centre of each column equals the difference between the sum of the top 2 numbers and the bottom two numbers.
