Aligning type to baseline the right way with SASS

_baseline.scss

$base-font-size: 	16px;
$base-line-height: 	1.5;

// this value may vary for each font
// unitless value relative to 1em
$cap-height: 		0.68;


@mixin baseline($font-size, $scale: 2) {

	// rhythm unit
	$rhythm: $base-line-height * $font-size / $scale;

	// number of rhythm units that can fit the font-size
	$lines: ceil(($font-size + 0.001px) / $rhythm);

	// calculate the new line-height
	$line-height: $rhythm * $lines / $font-size;

	// use the results
	font-size: $font-size;
	line-height: $line-height;

	$baseline-distance: ($line-height - $cap-height) / 2;



	// METHOD 1
	/////////////////

	// this method can relatively move down elements you may not want to
	// position: relative;
	// top: $baseline-distance + em;



	// METHOD 2
	/////////////////

	// if you use this mixin only on elements that have one direction margins
	// http://csswizardry.com/2012/06/single-direction-margin-declarations/
	// you can use this method with no worries. 
	// this method assumes the direction is down and the margin is $base-line-height
	padding-top: $baseline-distance + em;
	margin-bottom: $base-line-height - $baseline-distance + em;
}