David Barnett
For the Lost Knowledge crowd:

The very first issue of Fine Woodworking, Winter 1975, Volume 1, Number 1, the article, Hand Planes - The care and making of a misunderstood tool by Timothy E. Ellsworth, states:

"The chip breaker should be set back 1/64 to 1/16 inch from the cutting edge of the iron. The closer setting would be used for the very fine shavings on finish work and for hard-to-plane woods. Setting the chip breaker back 1/32 to 1/16 inch would be for rough work and large shavings."

1/64 inch is .4 mm (0.396875 mm), which is ballpark for Kato-Kawai. Not much later, as I recall, 1/100" (or .25 mm) was offered as an ultrafine setting, if not in FWW, in something else I have lying around.

Nothing new to see here, folks. Move along. Move along.