I created a new field with the following values in version 1.12.10 running in Windows 7.
Placement : System Details
Group : All Printers
I tried to edit a computer PC device (/index.php/devices/1) and find my new field.
It seems that the field can only associated to PC.
Can I create a field for a printer ?
This appears to be a bug. I'll see what I can do.