MF Digital PicoJet Mask Setting Guide - Manual (Page 2)

Measuring Inner Diameter (hub printable)
In the picture to the right, although this is a hub
printable disc, the measuring is done the same as the
above example. The inner diameter is determined
by measuring from the left side of hub where the
printable area ends to the right side of the hub where
the printable area begins again. Then noting what
the ending point is. In this case, a Centimeter ruler
was used and indicated the printable area ended on
2.3cm. This inner diameter in millimeters is 23mm.
Note: Its import to get the most accurate
measurement. Try placing your ruler as close to the
middle of the hub (from top to bottom) as shown in
the picture.