Additional filters are available to show or hide Available and used Used numbers.
In the above example i have set CON/001, CON/003, CON/004 as unavailable and CON/002 and CON/005 as available. This means when i assign a classification of conference to my catalogue record it will use CON/002 as the first available shelf reference. Once CON/002 and CON/005 have both been assigned the next one will be automatically generated as CON/006.
If you need to change the status for a number already marked as Available or Not Available you can enter the number you wish to change into the next number field and then click the appropriate button, this will change its status accordingly.