diff --git a/lib/xmet/series.py b/lib/xmet/series.py
index 9ca3cec..5694cfc 100644
--- a/lib/xmet/series.py
+++ b/lib/xmet/series.py
@@ -50,3 +50,8 @@ class Series(dict):
 
             if sign is intersection:
                 return v1, pair[0]
+
+    def nearest(self, key):
+        k = sorted(self.keys(), key=lambda k: abs(k-key))[0]
+
+        return self[k]