To determine the percentage lean of meat:
NOTE: This method would certainly get you close, but is completely uncomplicated.
Density of lean beef (from info by link below) is 0.96 grams/milliliter
1 US cup contains 240 milliliters
For 1 US cup of lean beef, the expected weight value would be 0.96 g/ml x 240ml
the result would be 230.4 grams.