Metric prefixes are widely used outside the system of metric units. Some measurements are reported in units derived from both customary and metric units. They both report a coverage metric, measured as a percentage. See also notions of metric space equivalence. Line graphs represent the variation of a value over another metric, such as time. This is displayed on tires beside its metric equivalent. Addition and multiplication are continuous in the metric topology. O-rings are available in various metric and inch standard sizes. Training on metric conversion was not universal. A Euclidean space is an affine space equipped with a metric. Some prefixes used in older versions of the metric system are no longer used. Thus, Flamm's paraboloid is useful for visualizing the spatial curvature of the Schwarzschild metric. Emissivity values are the appropriate metric for radiant barriers. This was a form of official metric pound. Processor grindings serve as the main metric for market analysis.