diff --git a/include/GFitsTableCol.hpp b/include/GFitsTableCol.hpp
index 9606f80..04620ef 100644
--- a/include/GFitsTableCol.hpp
+++ b/include/GFitsTableCol.hpp
@@ -71,7 +71,11 @@ protected:
     std::string m_name;        //!< Column name
     std::string m_format;      //!< Column format
     std::string m_unit;        //!< Column unit
-    int         m_colnum;      //!< Column number in FITS file (starting from 1)
+    int         m_colnum;      //!< Column number (starting from 1).
+                               //!< This parameter is used to signal if a
+                               //!< table column corresponds to a FITS file
+                               //!< column. If it is set to 0 there is no
+                               //!< correspondance.
     int         m_type;        //!< Column type
     int         m_repeat;      //!< Repeat value of column
     int         m_width;       //!< Width of column
diff --git a/src/GException.cpp b/src/GException.cpp
index 3eb6b8d..2c475a1 100644
--- a/src/GException.cpp
+++ b/src/GException.cpp
@@ -356,7 +356,7 @@ GException::fits_hdu_not_found::fits_hdu_not_found(string origin,
  * @brief FITS error: HDU not found in FITS file
  *
  * @param[in] origin Method that throws the error.
- * @param[in] extno Extension number (starting from 1).
+ * @param[in] extno Number of the extension that was not found.
  * @param[in] status cfitsio status.
  ***************************************************************************/
 GException::fits_hdu_not_found::fits_hdu_not_found(string origin,