diff --git a/src/main/java/fr/jmmc/oitools/meta/CustomUnits.java b/src/main/java/fr/jmmc/oitools/meta/CustomUnits.java
index e6bc03e..6bc9b01 100644
--- a/src/main/java/fr/jmmc/oitools/meta/CustomUnits.java
+++ b/src/main/java/fr/jmmc/oitools/meta/CustomUnits.java
@@ -47,6 +47,14 @@ public CustomUnits(final boolean required) {
         super("UNIT_CUSTOM", "");
         this.required = required;
     }
+    
+    /**
+    * Define the value of unit 
+    * @param unit other CustomUnits instance
+    */
+    public void set(final CustomUnits unit) {
+        set(unit.getStandardRepresentation());
+    }
 
     /**
      * Define the value of unit
diff --git a/src/main/java/fr/jmmc/oitools/model/OITable.java b/src/main/java/fr/jmmc/oitools/model/OITable.java
index ef0375f..51b2595 100644
--- a/src/main/java/fr/jmmc/oitools/model/OITable.java
+++ b/src/main/java/fr/jmmc/oitools/model/OITable.java
@@ -21,13 +21,10 @@
 
 import fr.jmmc.oitools.OIFitsConstants;
 import fr.jmmc.oitools.fits.FitsConstants;
-import fr.jmmc.oitools.fits.FitsHeaderCard;
 import fr.jmmc.oitools.fits.FitsTable;
-import fr.jmmc.oitools.fits.FitsUtils;
 import fr.jmmc.oitools.meta.ColumnMeta;
 import fr.jmmc.oitools.meta.KeywordMeta;
 import fr.jmmc.oitools.meta.Types;
-import fr.nom.tam.fits.HeaderCard;
 import java.util.logging.Level;
 
 /**
@@ -130,8 +127,9 @@ protected final void copyTable(final OITable src) throws IllegalArgumentExceptio
             }
         }
 
-        // Copy header cards:
-        if (src.hasHeaderCards()) {
+        // Copy header cards ?
+        // disabled for now (how to ensure consistency if the table is modified ?)
+        if (false && src.hasHeaderCards()) {
             // Copy references to Fits header cards:
             getHeaderCards().addAll(src.getHeaderCards());
         }
@@ -145,9 +143,17 @@ protected final void copyTable(final OITable src) throws IllegalArgumentExceptio
             columnName = column.getName();
             columnValue = src.getColumnValue(columnName);
 
-            if (columnValue == null) {
+            if (columnValue == null && !column.isOptional()) {
                 columnValue = createColumnArray(column, getNbRows());
             }
+            
+            // Copy custom units:
+            if (column.isCustomUnits()) {
+                final ColumnMeta srcColumn = src.getColumnDesc(columnName);
+                if (srcColumn != null && srcColumn.isCustomUnits()) {
+                    column.getCustomUnits().set(srcColumn.getCustomUnits());
+                }
+            }
 
             if (logger.isLoggable(Level.FINE)) {
                 logger.log(Level.FINE, "COLUMN {0} = ''{1}''", new Object[]{columnName, columnValue});