Now that this topic I had already forgotten has been resurrected, I should report that firmware updates on this thing will ruin the calibration at least on DC voltage ranges, or so I was told by a Gossen tech support (a guy actually called me when I asked them) so whenever a firmware upgrade is done, the meter should be recalibrated. Couldn't notice that any other range would be miscalibrated after the upgrade.
In fact the error due to this was quite subtle but still existing (but technically still in spec!). So contrary what I said before, mine was screwed similarly than Dave's Energy (DC ranges off by small but noticeable amount).
That is probably why they don't have any freely downloadable firmware on their web pages. I calibrated it back best I could using a calibrated 34401A as a reference and several power supplies but maybe I'll just someday send it to Gossen for a comprehensive calibration anyway.
I think if you leave the firmware upgrades (if you ever happen to need one) to Gossen to do them together with a calibration, then you'll be just fine.
Regards,
Janne