Well in one web page, I calculate the height of all header div, with $(elem).height(), well calculate the height of the header div for example, this give me 74px this is the real height of the div, but when I scroll the page or I load another page from the middle of the page, some times the height set of more 104px why this happen?
this is my code

<div class="header">
	<div class="header-left">
		<img src="images/logo.png">
	<div class="header-right">
		<div class="header-top">
		    <p><span class="phoneN"></span> <span><input type="text" class="searching"></span></p>
<div class="slider">
	<ul class="proslider">
		<li><img src="images/sliders + psd/sliders/slider1.png" width="100%"></li>
		<li><img src="images/sliders + psd/sliders/slider2.png" width="100%"></li>
		<li><img src="images/sliders + psd/sliders/slider3.png" width="100%"></li>

// In this code I calculate de height for the header, well the header have position: fixed 
// The thing is that the slider must have that value for margin top, and how I emplain before
// this goes crazy, sometimes this set for 104px and sometimes the real value wich are 74px
// , clear to my screen this value varies depending the resolution, but I try this in other screens
// and happen the same.