How to Use Surveyor's Chain Measurements

Invented by clergyman Edmund Gunter, the surveyor's chain made it possible to accurately measure distances and acreage in an era before global positioning satellites permitted mapping from space. The surveyor's chain made it possible for Lewis and Clark to map the Louisiana Purchase and lay out cities, townships and railroads. Here's an explanation of the measurements and how to use them.

Instructions

Difficulty: Moderately Challenging

Basic Units

1. Equate a standard surveyor's chain, or Gunter's chain, to 66 feet or 22 yards. There are also half-length chains of 33 feet. Equate an engineer's chain, or Ramsden's chain, to 100 feet.
2. Divide a surveyor's chain into 100 links, equal to 0.66 feet, or 7.92 inches. Gunter's original chain was made with 100 links, a half-chain with 50. A Pennsylvania surveyor's chain, while 66 feet long, is made with only 80 links.
3. Convert a measurement in surveyor's chains into rods by multiplying by 4, into furlongs by dividing by 10 and into miles by dividing by 80. Convert a length in surveyor's chains to meters by multiplying by 20.1168 and into kilometers by multiplying by 0.0201.

Making Measurements With Chains

4. Place tallying tags in the chain to subdivide it into 10 equal lengths.
5. Shoot a "line" from your starting point to the first visible object by sighting it with the circumferentor. If the object is indistinct, send a stakeman with an espontoon to the spot to provide a better sighting target.
6. Stand both chainmen next to you.
7. Send the fore chainman toward the object, pulling the chain to its full length. Signal the fore chainman to move left or right until he is precisely aligned with the sighting object.
8. Deposit a marking peg at the fore chainman's position.
9. Advance everyone toward the sighting object, keeping the chain taut. Stop at the site where the marking peg was laid. Repeat Steps 4 and 5, and then have the hinder chainman take up the peg at his position.
10. Repeat Step 6 until the hinder chainman has all the pegs or until the sighting object is reached. If the object is not reached, transfer the pegs to the fore chainman again. Repeat Steps 4 through 6 until the sighting object is reached. Record the distance in chains.

What to Measure With Chains

11. Mark the distance of railroad tracks, bridges and stations from a designated origin point in miles and chains. This is still done in Great Britain, despite the country's having gone metric, because the numbers generated are easier to remember.
12. Measure land distances on American farms using wheels a tenth of a chain in diameter.
13. Gauge the spread of wildfires in chains per hour.

Tips & Warnings

• By 1785 law, only Gunter's 66-foot chain was allowed for land surveying work.
• An acre of land is equal to 10 square chains. A square mile is equal to 640 acres or 6,400 square chains (80 chains on each side, 80 x 80 = 6,400).

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