This target is the inverse polarity of 2015a USAF target. That is, this target is covered in chrome and the tri-bar pattern is glass. Extreme resolution target, 1951 USAF from group 4 to group 11, element 6. Mounted in a colorful, hard to lose, metal, hard to break, microscope slide, suitable for challenging research grade microscope objectives including oil immersed NA/1.4. Chrome is about 1,000 angstroms thick. The target pattern is clear in the chrome background.