FlowType & EM Values

Elements that have a padding set with em will rescale on window reload and hence create an unpleasant jump.

HTML

<script src="https://ajax.googleapis.com/ajax/libs/jquery/1.11.3/jquery.min.js"></script>
<script src="https://cdn.rawgit.com/simplefocus/FlowType.JS/master/flowtype.js"></script>
<div id="nav-em-padding">Menu</div>
<div id="nav-px-padding">Menu</div>
<div id="nav-percentage-padding">Menu</div>

CSS

#nav-em-padding {
	display: block;
	margin: 0;
	padding: 0;
	font: 1.2rem Helvetica, Arial, sans-serif;
  padding-left: 0.6em;
  border: 4px solid slategrey;
  border-radius: 20px;
}

#nav-px-padding {
	display: block;
	margin: 0;
	padding: 0;
	font: 1.2rem Helvetica, Arial, sans-serif;
  padding-left: 60px;
  border: 4px solid slategrey;
  border-radius: 20px;
}

#nav-percentage-padding {
	display: block;
	margin: 0;
	padding: 0;
	font: 1.2rem Helvetica, Arial, sans-serif;
  padding-left: 6%;
  border: 4px solid slategrey;
  border-radius: 20px;
}

JavaScript

// jQuery v1.11.3
// on DOM ready

$('#nav-em-padding, #nav-px-padding, #nav-percentage-padding').flowtype({
  minFont   : 20, 
  maxFont   : 120,
  fontRatio : 6
});