contracts for difference, page-33

re: contracts for difference aussie 200 v spi So you can assume that the aussie 200 as it is called is directly related to the spi and that would be the reason for the drop from 4283 at the close to a sudden 4258
within 5 minutes.Of course if you were trading the aussie 200 during the day and had set stops under 4260 you would of been taken out.
One of the problems trading cfds on indices with market makers, this instrument mirrors its own design .If it is supposed to mirror something I wonder what it is? Can anyone enlighten me . my observations of it today are somewhat mystified. What is it actually a mirror of?