diff --git a/public/index.php b/public/index.php
index 7a36648..1cd0daa 100644
--- a/public/index.php
+++ b/public/index.php
@@ -10,31 +10,41 @@
 	<meta name="msapplication-TileColor" content="#00aba9">
 	<meta name="theme-color" content="#ffffff">
 <?php
+	function getPercentageUsed($total, $used) {
+		return ($total && $used ?
+			sprintf('%.4f', (100 * $used / $total))
+		: false);
+	}
+	function getDifference($minuend, $subtrahend) {
+		return ($minuend && $subtrahend ?
+			$minuend - $subtrahend
+		: false);
+	}
 	$hinamizawa_total = disk_total_space(/data/);
 	$hinamizawa_free = disk_free_space(/data/);
-	$hinamizawa_percent_used = $hinamizawa_total ?
-		(($hinamizawa_total - $hinamizawa_free) / $hinamizawa_total)
-	: false;
+	$hinamizawa_used = getDifference($hinamizawa_total, $hinamizawa_free);
+	$hinamizawa_percent = 
+		getPercentageUsed($hinamizawa_total, $hinamizawa_used);
 	$maebara_total = disk_total_space(/data/maebara/);
 	$maebara_free = disk_free_space(/data/maebara/);
-	$maebara_percent_used = $maebara_total ?
-		(($maebara_total - $maebara_free) / $maebara_total)
-	: false;
+	$maebara_used = getDifference($maebara_total, $maebara_free);
+	$maebara_percent = 
+		getPercentageUsed($maebara_total, $maebara_used);
 	$houjou_total = disk_total_space(/data/houjou/);
 	$houjou_free = disk_free_space(/data/houjou/);
-	$houjou_percent_used = $houjou_total ?
-		(($houjou_total - $houjou_free) / $houjou_total)
-	: false;
+	$houjou_used = getDifference($houjou_total, $houjou_free);
+	$houjou_percent = 
+		getPercentageUsed($houjou_total, $houjou_used);
 	$ryuuguu_total = disk_total_space(/data/ryuuguu/);
 	$ryuuguu_free = disk_free_space(/data/ryuuguu/);
-	$ryuuguu_percent_used = $ryuuguu_total ?
-		(($ryuuguu_total - $ryuuguu_free) / $ryuuguu_total)
-	: false;
+	$ryuuguu_used = getDifference($ryuuguu_total, $ryuuguu_free);
+	$ryuuguu_percent = 
+		getPercentageUsed($ryuuguu_total, $ryuuguu_used);
 	$sonozaki_total = disk_total_space(/data/sonozaki/);
 	$sonozaki_free = disk_free_space(/data/sonozaki/);
-	$sonozaki_percent_used = $sonozaki_total
-		(($sonozaki_total - $sonozaki_free) / $sonozaki_total)
-	: false;
+	$sonozaki_used = getDifference($sonozaki_total, $sonozaki_free);
+	$sonozaki_percent = 
+		getPercentageUsed($sonozaki_total, $sonozaki_used);
 ?>
 	<style type="text/css">
 		.pie {