"I don't have that model, but found this about setting the text line by line:
http://support.brother.com/g/b...
Is that what you are wanting to do?
Below is in the PT-D600 manual,, so if size is set to auto, it takes away the option to make the font large.
Setting Auto Fit Style
When [Size] is set to [Auto] and [Length] is set to a specific length, you
can reduce the text size to fit within the label length. When [Text Size] is
selected, the total text size is modified to fit within the label. When [Text
Width] is selected, the text width will be reduced to the size of x1/2
setting.
• The 6 point font only prints in Helsinki, no other font type.
• When [Size] is set to [Auto] and all the text is entered in uppercase,
the text is automatically adjusted to print in the largest font size
possible for each tape width. This font size is larger than the largest
font size available in the font settings for each tape width.
