The diagram contains two diamonds of 3x3 circles, arranged side by side, with the central 4 circles overlapping.

Starting in the central left circle of each diamond, the numbers from 1 to 9 are written in lines, moving up and to the right.

In the circles where the diamonds overlap, the values are added together to give the ones shown on the final diagram.

Add up the four outer numbers and place your answer in the centre square of the shape one place clockwise.

Split the grid in half vertically, to give two columns, 3 squares wide.

Working from top to bottom, left then right, and reading each 3 square row as a whole 3 digit number, the columns follow the sequence of square numbers, from 10 to 21.

Taking any series of 3 numbers in a straight line in the diagram, their total is always 19.

Working from the top row, add the values in adjacent boxes and put this sum in the box directly below, working towards the centre.

Repeat this pattern starting at the bottom row as well.