Working in rows, add together the numerical values of the left and right hand letters to give the numerical value of the central letter.

In each segment of the diagram are a pair of letters, one of which is the same distance from the start of the alphabet as the other is from the end.

The numerical values of the letters in opposite segments of the circle always add up to 17.

As you move down, the numerical value of the letters follows the sequence of Prime Numbers.

Writing each letter as its numerical value and working in rows, add the top 2 digit number to the bottom 2 digit number to give the 3 digit result in the centre.