As you can see in ZPL programming manual https://www.zebra.com/content/dam/zebra/manuals/printers/common/programming/zpl-zbi2-pm-en.pdf
The ^FB (Field Block) ZPL command has no any mention of font scaling feature. The only thing it describes is automatic increase or decrease of the block size upon a change of the font size.
As a workaround you may use scalable fonts. Then for each possible amount of delivery numbers in your field block your program can calculate needed font size and magnification factor. Then while printing your delivery numbers in a field block your program can setup font parameters that are corresponding to exact amount of numbers.
Software Engineer, Kutir Mobility
Posted on behalf of Zebra Technologies
Thanks for the response, I think that’s the way we have to go then.
We’re already putting some code together that, by working out how long the string of delivery numbers is, we can dynamically generate the ZPL to dictate font size.