Couple of mixins

mixins.scss

////
/// mixins.scss
/// Mixins
/// @author Ash Whiting
////

/// FONT SIZES IN REMS
/// Convert font sizes to rems with fallbacks
/// @param {size} $size - Font size in pixels
/// @param {line} $line - Line height in pixels
/// @example
/// @include fs(20,22)

@mixin fs($size: 1.6, $line: $size) {
	font-size: $size + px;
	line-height: $line + px;
	font-size: $size / 10 + rem;
	line-height: $line / 10 + rem;
}

/// RESPONSIVE HEADER TAGS
/// Calculate the least square fit linear regression of provided values
/// @param {map} $map - A SASS map of viewport width and size value combinations
/// @return Linear equation as a calc() function
/// @example
/// font-size: least-squares-fit((576: 24, 768: 24, 992: 34));

@function least-squares-fit($map) {
    $length: length(map-keys($map));
    
	@if $length < 2 {
		@error "leastSquaresFit() $map must be at least 2 values";
	}

	$resTotal: 0;
	$valueTotal: 0;

	@each $res, $value in $map {
		$resTotal: $resTotal + $res;
		$valueTotal: $valueTotal + $value;
	}

	$resMean: $resTotal / $length;
    $valueMean: $valueTotal / $length;
    
	$multipliedDiff: 0;
	$squaredDiff: 0;

	@each $res, $value in $map {
		$resDiff: $res - $resMean;
		$valueDiff: $value - $valueMean;
		$multipliedDiff: $multipliedDiff + $resDiff * $valueDiff;
		$squaredDiff: $squaredDiff + $resDiff * $resDiff;
	}

	$m: $multipliedDiff / $squaredDiff;
	$b: $valueMean - $m * $resMean;

	@return calc(#{$m * 100}vw + #{$b}px);
}