## How Many? A Dictionary of Units of Measurement © Russ Rowlett and the University of North Carolina at Chapel Hill Table of Contents About the Dictionary Using the Dictionary Z

Z
a common symbol for Universal Time. This symbol is often used with a 4-digit statement of the time in hours and minutes; thus 8:43 UT is written 0843 Z. The symbol is often pronounced "zulu," the name of the letter Z in the international radio alphabet.
z
symbol for redshift, a unit of relative distance used in astronomy.
zak
a Dutch unit of volume, now interpreted as a metric unit equal to the hectoliter (100 liters). The hectoliter is equivalent to 26.417 U.S. gallons, 21.999 British Imperial gallons, or 3.5315 cubic feet. This is a metric version of the British sack.
zentner (Ztr)
a traditional German unit of weight or mass, comparable to the traditional quintal and to the English hundredweight. Similar units were used in Scandinavia. Originally the zentner was equal to 100 pfund, or German pounds. 100 pfund varied from 110 to as much as 120 pounds avoirdupois (49.9-54.4 kilograms), depending on the market. After the introduction of the metric system in Germany, the zentner was redefined to equal to exactly 50 kilograms, which is about 110.231 pounds. In English, the zentner is commonly spelled centner.
zepto- (z-)
a metric prefix denoting 10-21 (one sextillionth). Adopted by the CGPM in 1990, the prefix is derived from the Latin septem, meaning 7, because this is the seventh prefix (n = 7 in 10-3n) in the SI system of metric prefixes. The s was replaced by a z to avoid confusion with the abbreviation for the second, which is an SI base unit.
zetta- (Z-)
a metric prefix denoting 1021 (one sextillion). The prefix was coined to parallel the prefix zepto-.
zettameter (Zm)
a metric unit of distance equal to 1021 meters or 1018 kilometers. One zettameter equals about 32.408 kiloparsecs (kpc) or 105 702 light years. This is a little more than the diameter of the Milky Way galaxy in which we live.
Zhubov scale
a scale for reporting ice coverage of polar seas; see ball.
zoll
the traditional German inch, equal to 1/12 fuss. Originally the zoll was equal to 1.037 inches (about 2.634 centimeters). In Switzerland, it is now considered a metric unit equal to exactly 3 centimeters (1.1811 inches). There's no change in the plural.