Basic specific gravity, definition

For clarification, it is necessary to understand the basic definitions that are used (1) density is the mass of liquid per unit volume at 15.6°C (60°F), (2) relative density is the ratio of the mass of a given volume of liquid at 15.6°C (60°F) to the mass of an equal volume of pure water at the same temperature, and (3) specific gravity is the same as the relative density and the terms are used interchangeably. 

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