It may rarely happen that you have to install a DEIMOS removable element which (a) has never been barcoded or (b) has a lost or damaged barcode label.
The most likely elements to show up without barcode labels are filters brought by observers. Gratings for DEIMOS are so expensive that it seems unlikely observers will bring their own, but our filters are fairly standard and it's possible that an observer will bring their own filter.
It's also possible, though unlikely, that a bar code label will get damaged. These labels are metal (3 thou aluminium) and the barcode and character label is anodized rather than inked onto the surface. It should take serious abuse to render these labels unscannable. However, things do happen. It is even less likely, though possible, that a label will come off. The adhesive is heavy duty and rated for freezing, vacuum, etc.
For existing filters and gratings with damaged labels there is a workaround. You can scan the emergency backup label on the laminated sheet of barcodes affixed to the instrument. So for example, if the barcode on grating 830G has become damaged, you can scan "830G" label on the emergency barcode sheet.
For a foreign filter or grating with no barcode label, there is no recourse except manual configuration using tkremel or a text editor. Slitmasks with damaged or missing labels also require manual configuration. An unscannable or missing mask label will confuse the auto-mask-scan code horribly.
See the Manual Configuration Guide for instructions on fallback methods of configuring DEIMOS.
de@ucolick.org