Eighty is four score and reduces to eight. Its scriptural anchor is the age of Moses at the Exodus: he was eighty and Aaron eighty-three when they stood before Pharaoh, so eighty marks the beginning of Moses's public work, late in a long life. Psalm 90, ascribed to Moses, gives the span of human years as threescore and ten, or by reason of strength fourscore, seventy or with vigour eighty, so eighty is the outer measure of a strong life. In Hebrew the letter pe carries the value eighty.
In chemistry, eighty is the atomic number of mercury, the only metal liquid at ordinary temperature; its symbol, Hg, comes from the Latin hydrargyrum, water-silver, itself from Greek, while the English name honours the swift-moving Roman god.
Eighty factors as 2^4 x 5 and carries 10 divisors in all. Summing its proper divisors gives 106, more than the number itself, which makes it an abundant number in the classical sense the Pythagoreans used to sort integers into deficient, perfect and abundant classes.
Florence Campbell, a student of Balliett's, restated and extended the chart in Your Days Are Numbered in 1931, and Juno Jordan, founder of the California Institute of Numerical Research, standardised the modern four-part chart of life path, expression, soul urge and personality numbers in 1965; both writers worked from name and birth date rather than from any older number philosophy.