Aah I see! What you need to know is that the food optimising book just has average syn values for foods. So an average cereal bar will be 4.5 syns while individual brands will vary widely with some being less (like the alpen lights) and others being higher (like a quaker oats one).
In the book fruit yoghurts are half a syn but we all know that many are actually free. So it is best to check for that particular brand just to make sure.