diff --git a/README.md b/README.md
index 0bc024bc4d6f9268923e81452ab4669db2285294..e122c523032db392f7cc58c708807ac8e2caa3be 100644
--- a/README.md
+++ b/README.md
@@ -20,6 +20,7 @@
 * [About the Project](#about-the-project)
   * [Built with](#built-with)
 * [Usage](#usage)
+  * [Validity ranges](#validity)
 * [License](#license)
 * [Contact](#contact)
 * [Acknowledgements](#acknowledgements)
@@ -53,14 +54,18 @@ The current release of the proton response files is based on:
 
 * The RMF and ARF files can be loaded with any X-ray analysis software compliant with the NASA caldb format.
 * Since the accuracy of the Geant4 modeling of the proton stopping power degrades below 1 keV (20% at 1 keV reported in the Geant4 Physics Reference Manual), the energy redistribution is modelled from 1 keV to the upper threshold of the instrument X-ray RMF.
-* Validity energy range: due to biases at the boundary of the RMF modeling, induced by features in the interpolation because of limited statistics in the simulation, the spectral analysis must be performed within the following intervals:
-  * MOS: 1.5 - 11.5 keV
-  * PN: 1.5 - 20 keV
-
 * The response files are available for three optical filters: 
   * thin: 0.16 um of polyimide and 0.04 um of aluminium
   * medium: 0.16 um of polyimide and 0.08 um of aluminium
   * thick: 0.33 um of polypropylene, and 0.11 um of aluminium, and 0.045 um of tin
+  
+### Validity ranges
+
+Due to biases at the boundary of the RMF modeling, induced by features in the interpolation because of limited statistics in the simulation, the spectral analysis must be performed within the following intervals:
+* MOS: 1.5 - 11.5 keV
+* PN: 1.5 - 20 keV
+
+
 
 
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