The backstraps are two different thicknesses and two different patterns (a cross-hatch pattern similar to the sides of the grip, and horizontal lines similar to the front of the grip).
Theoretical work has also shown that certain rotating gravastars are mathematically stable assuming certain angular velocities, shell thicknesses, and compactnesses.
Layer thicknesses are chosen to produce destructive interference in the beams reflected from the interfaces, and constructive interference in the corresponding transmitted beams.
Both countries use the metric system in building, and plasterboard is manufactured in thicknesses of 10mm, 13mm, and 16mm, and sometimes other thicknesses up to 25mm.