13th
Second Light provides a second layer of information to the Microsoft surface. TheĀ projection surface alternates between opaque and transparent. The projected image also alternates between two images. One appears on the surface, the other goes up through the surface to fall on anything above the table, such as a piece of tracing paper. At the moment the second projected image is predetermined although I’m sure it’s not a large step to recognise different viewers and project different information to them at the same time, e.g. a text viewer, an xray viewer, etc.
Article on it with PCMag.