a metric ruler is a ruler with metric units
metric_system is metric_unit_of_measure. metric_system is unit_of_measure. metric_ton is metric_weight_unit. metric is one_system_of_units_of_measurements. euclidean_metric is metric. metric_linear_unit is metric_unit. meter is metric_linear_unit. ruler is distance_measuring_device. metric_system is not metric_unit_of_measure. metric_unit_of_measure is metric_system.