“Tokyoflash’s latest Kisai watch is the Kisai Stencil, based on a concept design submitted by a math teacher named Heather Sable. It uses “negative space” to draw the numbers, a display that is cryptic at first but is easy to read at a glance once you’ve figured out the knack of it.” — Tokyoflash’s Kisai Stencil watch: telling the time with negative space - Boing Boing