If you have set up more than one number series code for the same kind of basic information or transactions, you can create relationships between the codes. This feature can assist you in deciding among the codes when you use a number.
Open the 
No. Series window.
Select the line with the number series you want to create relationships for.
Click Series, Relationships.
Click the Series Code field, and then click
the AssistButton 
to see the No.
Series window.
Select the relevant number series code, and then click OK to copy it to the field.
Repeat steps 4 and 5 on a separate line in the window for each code you want to relate to the selected number series.
Now when you set up something that requires a number, you can use the relationships you created to select among the related number series.
This procedure creates relationships only for the number series you selected in the Number Series window in step 2. To create relationships for other number series, you must repeat the entire procedure for each relevant number series.