Modular scale for font sizing with power math function

ms.scss

// http://www.modularscale.com/
// http://webdesign.tutsplus.com/articles/how-to-establish-a-modular-typographic-scale--webdesign-14927
@function pow ($x, $n) {
  $ret: 1;

  @if $n >= 0 {
    @for $i from 0 to $n {
      $ret: $ret * $x;
    }
  } @else {
    @for $i from $n to 0 {
      $ret: $ret / $x;
    }
  }

  @return $ret;
}

@function ms ($n, $base: $ms-base, $ratio: $ms-ratio) {
  @return pow($ratio, $n) * $base;
}