You have opened a project. Options > Settings > Projects > "Project name" > Devices > Numbering (online). Click [...] next to the Numbering format field in the Settings: Numbering (online) dialog. Select a user defined scheme from the Numbering formats dialog. In the DT or Designations tab, click [...]. Double-click a format element in the DT format dialog.
In this dialog you can edit format elements that can be part of the numbering format.
Overview of the main dialog elements:
The value in this field defines how many positions must be used.
Missing positions are filled in with this filler character.
(Only for format elements of the "Counter" type)
Here you can enter the value with which the device numbering should start. Allowed values are 0-X.
(Only for format elements of the "Counter" type)
If this check box is selected the alphanumeric counter is used. If not, a numerical counter is used.
(Only for format elements of the "Counter" type)
When using the alphanumeric counter specify the characters here that are allowed to be used by the counter. Only alphanumeric characters are allowed.
Alphanumeric counters are sorted by character from left to right (in the same manner as Excel columns). If you have specified for example the characters "AKS", then counting proceeds as follows:
See also
Specifying Online Numbering Format
Automatically Numbering New Devices