diff --git a/src/indexbuffer.cpp b/src/indexbuffer.cpp
--- a/src/indexbuffer.cpp
+++ b/src/indexbuffer.cpp
@@ -1,5 +1,5 @@
 /*
-  Copyright © 2017 Hasan Yavuz Özderya
+  Copyright © 2018 Hasan Yavuz Özderya
 
   This file is part of serialplot.
 
@@ -47,3 +47,15 @@ Range IndexBuffer::limits() const
 {
     return Range{0, _size-1.};
 }
+
+int IndexBuffer::findIndex(double value) const
+{
+    if (value < 0 || value > size() - 1)
+    {
+        return OUT_OF_RANGE;
+    }
+    else
+    {
+        return value;
+    }
+}