sentences:  times smaller than the relative uncertainty for itself.can be found out only by dividing the "G" product by "G", and "G" is known only to a relative uncertainty of (2014 NIST recommended value), so will have the same uncertainty at best.For this reason and others, astronomers prefer to use the un-reduced "G" product, or mass ratios (masses expressed in units of Earth mass or Solar mass) rather than mass in kilograms when referencing and comparing planetary objects.