Previous second block

No idea. What kind of blocks are you talking about and how are they arranged spatially and/or temporally?

Block in this case is the method that we divide set data points in several portion.

Why do you think that you need both 'previous' and 'second'?

It is because in order to compute the solution in the currenct block, it involve the set data points in the previous two block where the point x is located at the previoius second block. I hope my explanation is clear..

Oh, not really, but perhaps this will work:

Since it contains the point X, which is located in the second block preceding, the ...

I have already told you to stop using 'hence' because you always misuse it. You have misused it again here. If you are not going to follow my advice, then I hardly have reason to continue offering it.

If I am not mistaken, the word since always followed by hence right?

Not at all! Since means hence; they just preface different clauses.