Well then you either slice a brick open diagonally and measure it or you just stick two bricks together and then......well place one brick on any of those bricks (please use super glue so bricks don't move). Now if we suppose that there is an imaginary brick on the single brick compared to the stack of 2, we can easily measure the distance through that imaginary brick because it doesn't exist but there are three other known bricks which provide the dimensions for us. Like from the top of brick stacked on top of one brick, passing through the imaginary brick with ends at the top of the brick with the imaginary brick on top of it. That way we'll have the diagonal of the imaginary brick. And the imaginary brick is dictated by the other solid bricks so its' diagonal will always be equal provided that given three bricks are 100% congruent. Did you get all that? OTL