Doped, pyrogenically prepared oxides of metals andor non-metals which are doped with one or more doping components in an amount of 0. A range of colors are thus viewable by rotating the interferometric modulator relative to an observer. The fluid delivery system may be modular. The pontoon boat is held rigid by first and second underbars. The layout of the gauge permits multiple sensors to be mounted in a compact gauge housing and the gauge housing, in turn, may connected to a robotic arm for rapid and repeated use as an automated measurement apparatus for a component assembly line.