diff --git a/plotjuggler_base/include/PlotJuggler/reactive_function.h b/plotjuggler_base/include/PlotJuggler/reactive_function.h
index 601cfe43e..cf05e4229 100644
--- a/plotjuggler_base/include/PlotJuggler/reactive_function.h
+++ b/plotjuggler_base/include/PlotJuggler/reactive_function.h
@@ -27,6 +27,8 @@ struct TimeseriesRef
 
   double atTime(double t) const;
 
+  int getRawIndexAtTime(double t) const;
+
   unsigned size() const;
 
   void clear() const;
diff --git a/plotjuggler_base/src/reactive_function.cpp b/plotjuggler_base/src/reactive_function.cpp
index 27d54d1bf..b861b87ec 100644
--- a/plotjuggler_base/src/reactive_function.cpp
+++ b/plotjuggler_base/src/reactive_function.cpp
@@ -114,6 +114,7 @@ void ReactiveLuaFunction::prepareLua()
   _timeseries_ref["at"] = &TimeseriesRef::at;
   _timeseries_ref["set"] = &TimeseriesRef::set;
   _timeseries_ref["atTime"] = &TimeseriesRef::atTime;
+  _timeseries_ref["getRawIndexAtTime"] = &TimeseriesRef::getRawIndexAtTime;
   _timeseries_ref["clear"] = &TimeseriesRef::clear;
 
   //---------------------------------------
@@ -190,6 +191,11 @@ double TimeseriesRef::atTime(double t) const
   return _plot_data->at(i).y;
 }
 
+int TimeseriesRef::getRawIndexAtTime(double t) const
+{
+  return _plot_data->getIndexFromX(t);
+}
+
 unsigned TimeseriesRef::size() const
 {
   return _plot_data->size();