This is taken from a 2011 email the Duke sent me long before we started the blog. He gave no sources or references and several google searches reveal nothing. If anyone knows the source, please contact me.
The Stanley company was (and remains) the world's largest tool manufacturer. Its markets were not solely in the United States and Canada but were found throughout the world. To meet the demands of foreign countries, especially those countries using different units of measurement, Stanley manufactured rules specifically for those markets. Folding rules made with metric measurements (boxwood two- and four-fold rules) were manufactured by Stanley as early as the 1860s. When Stanley began to manufacture Zig-Zag rules in 1899, it was only natural that the company should consider making metric models available. Stanley first offered a metric Zig-Zag in 1901.During the period of the Spanish Empire (1513-1834), standard measuring systems were mandated many times for its provinces, including Mexico, but the local governments generally ignored the mandates, causing confusion and disruption in commercial trading. Uniformity began when Mexico and Spain adopted the metric system in 1807, but prior to that, linear measurements called Burgos were used. The standard for this length was kept in Burgos, Spain, and thus the name. One Burgos was equivalent to 15/16 of an English inch.
The Spanish-speaking colonies, including Mexico and countries in Central and South America, used the Burgos system of measurement. California, which had been a part of Mexico from 1828 until 1846 when it declared itself an independent republic, (it gained statehood in 1850), also used this measurement. When the metric system was adopted by Spain and Mexico, it took years for people throughout these countries to change to the new system. Thus, Stanley manufactured a number of different models of Zig-Zag rules with three scales, English, metric, and Burgos, for that market.
The “Vara,” or the “Spanish yard,” comes from the Latin word “Forked Stick.” The origin of the vara has been traced to and substantially used over the centuries by the ancient Phoenicians, Egyptians, and especially the Romans. Early units of measurements derived from physical dimensions of the human body. Specifically the vara was determined by totaling the distance of four spans of the hand or one-quarter vara, from the tip of the thumb to the tip of the little finger or “handsbreadth.” Adopted by Spain’s official legislation in the late Sixteenth Century, a royal decree created a standard length of measurement known as “Vara of Burgos,” later known throughout the Hispanic world as the “Castilian Vara.” This same vara equaled Tres Pies (three feet), and a Legua (league) equaled 5,000 varas or approximately 2.6 miles.
When the colonists arrived to the New World they found the need to measure land, architectural layout, textile goods, furniture making and artwork such as Santos. Historical Spanish documents show that the vara measurement was used in Nuevo España as early as the middle Seventeenth Century through the end of the Nineteenth Century, and into the Americas as early as the Sixteenth Century. One such vara stick measuring 33 1/3 inches dates back as early as 1760 and was specifically used in Doña Ana County in southern New Mexico. It is now on display in the Museum of New Mexico at the Palace of the Governors. This measurement was also used and adopted in Texas in some old surveys, commonly known as “Spanish Land Grants.” This measurement was done by horseback by counting the horses pace or measuring the gate which came out to be about 33.333 inches or 2.7778 feet. Other measurements used in the Southwest were the adopted Mexican vara of 32.99 inches or 2.7492 feet. Lands held in “Public Domain” used the value of 33.372 inches or 2.7810 feet. In some remote villages in Northern New Mexico, the value of 33.069 inches or 2.7558 feet or four handsbreadth was used as their system of measurement. Shown here is just a small list of the vara measurements derived from the ancient Vara of Burgos. By the end of 1846 this system of measurement was soon discarded for the English system of measurement of miles, yards, feet, and inches. In 1895 the vara officially continued to be used until President Don Porfirio Díaz decreed the substitution of the Continental European Metric System. The vara remains with us to this day and it remains a measurement of interpretation and further research.
Another fascinating line of Zig-Zag rules that Stanley manufactured were the Cyrillic rules in Werschock and Sajen, pre-Revolutionary Russian (1917) units of measurement. According to Webster's Unabridged Dictionary, Sajen is a Russian measure of about seven English feet. For Sajen units, an English rule 7 feet long was divided into 100 parts, making each part approximately 7/8 inch. A 7-foot rule in Werschock units was divided into 48 equal parts, which is about 1 ¾ inches per segment. Russia officially changed from the old system to the metric system after 1917. The government set a time-table for the institution of the metric system, but the old measurements continued in use.