# Bug in Effective distance

In the above link, it is mentioned that the effective distance between Element A and Element C is 30px.

Actually,the effective distance between Element A and Element C when both of them are placed one upon other is the sum of the bottom margin of Element A and the top margin of Element C.
now the bottom margin of element A is 10 px and the top margin of Element C is 30 px,So the effective distance between 40px.
but it is mentioned that the effective distance is 30px,

regards,
vignaan vardhan

no, its not. Because the bottom margin collapses. So the effective distance is 30px

which one should we consider the space of element A or Element c?

this is literally explained within the lesson:

Unlike horizontal margins, vertical margins do not add. Instead, the larger of the two vertical margins sets the distance between adjacent elements.

so if its element A or C depends on which has the larger margin. In this case, C has the larger margin, thus this will be the margin between the two elements.