Make a span() function for blueprint that returns the width in pixels of $n columns.

frameworks/blueprint/stylesheets/blueprint/_grid.scss

@@ -108,16 +108,20 @@ $blueprint-container-size: $blueprint-grid-outer-width * $blueprint-grid-columns
   @include column-base($last);
   @include span($n); }
 
+// Return the width of `$n` columns.
+@function span($n) {
+  @return $blueprint-grid-width * $n + $blueprint-grid-margin * ($n - 1);
+}
+
 // Set only the width of an element to align it with the grid.
 // Most of the time you'll want to use `+column` instead.
 //
 // This mixin is especially useful for aligning tables to the grid.
-@mixin span($n, $override: false) {
-  $width: $blueprint-grid-width * $n + $blueprint-grid-margin * ($n - 1);
-  @if $override {
-    width: $width !important; }
+@mixin span($n, $important: false) {
+  @if $important {
+    width: span($n) !important; }
   @else {
-    width: $width; } }
+    width: span($n); } }
 
 // The basic set of styles needed to make an element
 // behave like a column: