diff --git a/src/pvt_model/pvt_system/pvt_collector/__utils__.py b/src/pvt_model/pvt_system/pvt_collector/__utils__.py
index c1d428d..94f063e 100644
--- a/src/pvt_model/pvt_system/pvt_collector/__utils__.py
+++ b/src/pvt_model/pvt_system/pvt_collector/__utils__.py
@@ -161,6 +161,10 @@ def reflectivity(self) -> float:
 
         """
 
+        # FIXME: I'm not convinced that this calculation is correct...
+
+        return 1 - self.absorptivity - self.transmissivity
+
         return sqrt(1 - self.absorptivity**2 - self.transmissivity**2)
 
     @property