Short answers, pulled from the story.
The symbol M Earth represents a specific quantity of matter equal to the entire planet we inhabit. Astronomers use this standard unit to compare other worlds, from rocky terrestrial planets to distant exoplanets orbiting faraway stars.
Pierre Bouguer and Charles Marie de La Condamine conducted experiments between 1737 and 1740 on Pichincha Volcano and mount Chimborazo in Ecuador and Peru. They detected a deflection of 8 seconds of arc but lacked the precision needed for a definitive density calculation.
Henry Cavendish performed his famous laboratory experiment in 1798 to measure gravitational attraction between two bodies directly. He derived Earth's mass by combining Newton's second law with Newton's law of universal gravitation using specific equations for gravity.
The Moon contributes about 1.2% of our planet's total weight, meaning the combined Earth-Moon system weighs slightly more than Earth alone. This value equals approximately six ronnagrams, or 6.0 Rg when using metric prefixes.
The primary source of error in current Earth mass calculations remains the gravitational constant known as G. Since at least the 1960s, uncertainty has been entirely due to difficulties measuring this fundamental physical constant accurately.