diff --git a/web/public_php/admin/functions_tool_graphs.php b/web/public_php/admin/functions_tool_graphs.php
index cd7e6b1d6..a7695147f 100644
--- a/web/public_php/admin/functions_tool_graphs.php
+++ b/web/public_php/admin/functions_tool_graphs.php
@@ -317,7 +317,7 @@
 
 			$val_data = explode(' ', $tmp_data[2]);
 
-			$result['ref'][] = $tmp_data[1] - $base;
+			$result['ref'][] = trim($tmp_data[1]) - $base;
 			$result['val'][] = trim($val_data[1]);
 		}