diff --git a/module_dfu/doc/factory_image.rst b/module_dfu/doc/factory_image.rst
index bd331d5e..a5f89ce9 100644
--- a/module_dfu/doc/factory_image.rst
+++ b/module_dfu/doc/factory_image.rst
@@ -12,6 +12,10 @@ Use the XMOS Development Tools to run the command:
 
   ``xflash --boot-partition-size 0x20000 usb_audio.xe``
 
+  Where the size passed using the ``--boot-partition-size n`` argument specifies
+  in bytes the minimum size required to store the boot loader, factory image and
+  any upgrade images.
+
 This programs the factory default firmware image into the flash device.
 The device will now support the DFU mechanism, and can use it to safely receive
 firmware updates, as well as revert to the factory firmware image when required,
@@ -26,7 +30,20 @@ image:
 
 To generate the firmware upgrade image run the following command:
 
-  ``xflash --upgrade 1 usb_audio.xe 0x20000 -o new_firmware.bin``
+  ``xflash --factory-version 13 --upgrade 1 usb_audio.xe 0x20000 -o new_firmware.bin``
+
+  Where the tools version passed using the ``--factory-version version``
+  argument specifies the version of the tools used to create the factory image.
+  This should be passed as ``12`` for images created using tools versions 10, 11
+  and 12.
+
+  The ``--upgrade id xe-file [size]`` argument specifies xe-file as an upgrade
+  image with version ``id``. Each version number must be a unique number greater
+  than 0.
 
 You should now have the file ``new_firmware.bin`` which contains the
 firmware with the newly specified Device Version Number.
+
+For further details on the use of XFLASH to create factory and upgrade firmware
+images please see the XFLASH Command-Line Manual section of the
+`xTIMEcomposer User Guide <https://www.xmos.com/published/xtimecomposer-user-guide>`_.