I use the disk behind the chuck method with either drilled holes, notches
in the rim, or visually aligning lines on the disk with a guide block
clamped to the lathe bed. To arrive at precise spacing of
holes/notches/lines, I either make something on the computer and glue the
printout to the disk, or I use the tape method. The tape method is down
and dirty but works amazingly well. I wrap a piece of masking tape around
the edge of the disk and cut it precisely so there is no overlap. Then I
peel the tape off the disk and lay it straight on the lathe bed. I
measure the total length (in millimeters for easy math), divide by the
number of divisions I want, make pencil marks on the tape, and wrap it
back around the disk. To transfer the divisions to the disk I line up the
tool rest to the center line and mark with a pencil. For one-time use I
skip making a disk and put the tape directly on the bowl or hollow form I
am working on. Works great.

-mike paulson, fort collins, co