The duration of 9 192 631 770 periods of the radiation corresponding to the transition between the two hyperfine levels of the ground state of the cesium 133 atom

Originally, the distance a Roman legion could march in 1000 paces. Now equal to 8 furlongs, 80 chains, 320 rods, 1760 yards or 5280 feet.

Distance equal to 0.9144 of a meter

Mean distance from the center of the Earth to the center of the Sun (a little less than 150 million km)

Amount of a substance equal to the number of atoms of Carbon-12 in 0.012 kilograms

Unit of time equal to the interval between two arrivals of the Sun at the Tropic of Capricorn

Force needed to accelerate a mass of 1 kg at 1 meter per second per second

Definition

Measurement

Length of the path traveled by light in a vacuum during a time interval of 1 / 299 792 458 of a second

Heat needed (at a pressure of one atmosphere) to raise the temperature of one gram of water by 1 degree Celsius

1/100 of the difference between the freezing and boiling points of water

Distance a star shifts position by 1 arcsecond during the time Earth moves 1 a.u. perpendicular to the star (less than 12 is a great Kessel run)

Originally, defined as the mass of 1 cubic centimeter of pure water

The number of electrons surrounding an uncharged atom (also = number of protons in its nucleus).