The problem-oriented discussions in this series mention many observations, experiments, and modelings that are needed to carry out the goals of the Planet Earth Initiative. The next logical step would be to compile from these mentions an enumeration of measurables (for example, cloud coverage and ocean surface temperature), with a view to specifying the instruments, platforms, spacings, frequencies, etc., at which these measurements should be made. This step has already been taken for significant fractions of the problems discussed. Tables 1 and 2 are outlines of such a compilation, the most comprehensive but not the most detailed, drawn from the 1988 National Research Council/Space Science Board report, Space Science in the Twenty-First Century: Mission to Planet Earth. Its emphasis is on the global approach, and some might argue that 10,000 “simple ground installations” are too few for such efforts as studies of crustal motion.