chains (ch) to Mils (mil) conversion

What is the chain?

The chain (ch) is a unit of length in the imperial and US customary systems, equal to 66 feet, traditionally used in surveying and land measurement.

Definition

One chain equals 66 feet, or 22 yards, or 4 rods.

$$1\ \text{ch} = 20.1168\ \text{m}$$

There are 80 chains in a mile and 10 square chains in an acre. This value uses the international foot; the US survey chain is larger by a factor of 1200/1199, giving about 20.11684 m.

Origin and History

The chain is named for Gunter's chain, a physical measuring device introduced by the English clergyman and mathematician Edmund Gunter around 1620. It consisted of 100 iron links totalling 66 feet, elegantly bridging the traditional (base-4/16.5) and decimal systems: distances could be recorded in decimal links yet still yield whole numbers of acres and miles. It became the standard tool of English and American surveyors for centuries.

Law and Notable Facts

The chain underpins the US Public Land Survey System, in which section lines and township grids were laid out in chains. A cricket pitch measures exactly one chain (22 yards) between the wickets—a lasting everyday trace of the unit. The chain is now largely obsolete outside historical land records and cricket.

Real-World Examples and Conversions

• A cricket pitch is 1 chain = 22 yards = 66 ft long.
• 1 chain = 100 links = 4 rods = 20.1168 m.
• 80 chains = 1 statute mile.
• An acre is 1 chain by 10 chains (10 square chains).

What is Mils?

Mils, also known as thou, is a unit of length commonly used in engineering and manufacturing, particularly in the United States. Understanding its definition and applications is crucial in various technical fields.

Definition of a Mil

A mil is defined as one thousandth of an inch. It is a small unit of length, often used when dealing with precise measurements.

$$1 \text{ mil} = \frac{1}{1000} \text{ inch} = 0.001 \text{ inch}$$

In metric units:

$$1 \text{ mil} = 0.0254 \text{ mm} = 25.4 \text{ μm}$$

Formation and Origin

The term "mil" is derived from "milli-inch," emphasizing its relationship to the inch. It was developed to simplify calculations and communication in industries where precision is paramount. Instead of dealing with fractions of an inch, engineers and manufacturers could use whole numbers of mils.

Applications of Mils

Mils are used extensively in various industries:

• Electronics: Measuring the thickness of wires, circuit boards, and coatings. For example, the thickness of the copper layer on a printed circuit board (PCB) might be specified in mils.
• Manufacturing: Specifying the thickness of plastic films, sheet metal, and other materials.
• Paper Industry: Indicating the thickness of paper and card stock.
• Coatings: Measuring the thickness of paint, varnish, and other protective layers on surfaces.

Real-World Examples in Other Quantities

While mil primarily measures length, it influences other quantities:

• Area: The cross-sectional area of wires is sometimes expressed in "circular mils" (CM), especially in electrical engineering. A circular mil is the area of a circle with a diameter of one mil.

  • $$A = d^2$$

  • Where $A$ is the area in circular mils and $d$ is the diameter in mils.
• Volume: Though less common, mil can be used to derive volume measurements when combined with other units.

Notable Associations

While no specific law or person is directly associated with the formal definition of a mil, its adoption and standardization have been driven by industry needs and engineering practices. Organizations like the American National Standards Institute (ANSI) contribute to defining and maintaining standards that include the use of mils.

Additional Resources

For more information about mils, you can refer to the following resources:

• Thousandth of an inch - Wikipedia
• Circular mil - Wikipedia