# The same height of text in a large document

I’m typesetting a large document that contains a lot of mathematics. The only problem is that the height of text on some pages that ends with a displayed formula is less than (about 3-6mm) the height of pages that ends normally (without displayed formula).
I want that the height of text on all of my pages is quite the same. Does anybody know how to solve this problem? Is there any command that I should use in those pages in order to solve the problem?
By the way, I’m using options `a4paper`, `twoside` and `book` class in my document.

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Are you using `\raggedbottom` by any chance? Try to explicitly set `\flushbottom` very late in your preamble and see if it changes anything. Note that `\flushbottom` is the default for `book`. –  Martin Scharrer Apr 7 '11 at 10:22
@Martin: I've tried both `\raggedbottom` and `\flushbottom`, but they don't change anything. BTW, what do you mean very late? –  user4669 Apr 7 '11 at 11:41
With "very late" I meant at the end of the preamble. –  Martin Scharrer Apr 7 '11 at 11:48
@Martin: thanks for your reply. I tried that, but it doesn't work. –  user4669 Apr 7 '11 at 18:49
contrary to what Ian Thompson said, the `\belowdisplayskip` is removed if it falls at a page break, so you should try providing a minimal example. –  egreg May 8 '11 at 9:43

I think this is caused by the fact that a vertical space is inserted after each displayed equation. The size of this space is controlled by `\belowdisplayskip`. Have a look at section 11.5.1 of Mathmode.pdf.
There were some discussions of `\cleader` in some recent questions, which might help a little bit. –  Bruno Le Floch Apr 8 '11 at 5:09