TARDIS were not, its weight would shatter the Earth's surface. In the tie-in novels, the interior of the TARDIS has been known to contain an entire city, encompass an entire parallel Earth, and even dwarf Gallifrey itself when turned inside out. A distinctive architectural feature of the TARDIS interior is the roundel. In the context of the TARDIS, a roundel is a circular decoration that adorns the walls of the rooms and corridors of the TARDIS, including the console room. Some roundels conceal TARDIS circuitry and devices, as seen in the serials "The Wheel in Space" (1968), "Logopolis", "Castrovalva" (1981), "Arc
Royal Air Force roundels be the same width as the blue, but on Spitfires with their narrower fuselages a thinner ring was acceptable. Also in May, an order was made to put red, white, and blue roundels on the underwings of all fighters, with an addendum that where the roundel was on a black background it should be outlined in yellow. In June, orders were given for the half black/half-white underwing scheme to be replaced by "sky" Underwing roundels were dispensed with until August when they were ordered back. Because of the pressures of front-line service there were always exceptions to the standards set