Many of you have attended a surveyor's convention and looked at the historical survey equipment on display. Often, the historical items are missing essential parts and would be impossible to use on a survey today. Most pieces of historical equipment carry a layer of dirt and tarnish prized by collectors of antiques. In fact, collectors are frequently told not to polish or restore their items because doing so devalues the equipment. At a survey convention many years ago, I asked a surveyor how a scale scribed on the side of a historical instrument in his collection worked. His reply was, "I never study the instruments; I collect them for the value." What a shame.
When I look at a historical instrument, I hear it calling out to me. "Understand me, study me, for I am your roots! Everything you survey today is tied to me. You as a surveyor cannot separate yourself from the work I performed." One of the instruments that speaks to me this way is the Goldsmith Chandlee compass. Chandlee was an American clockmaker who lived from 1751-1821, and the instruments he made are renowned for their excellent workmanship and design.
Investigating the ScaleFor years, I have seen all kinds of special scales and verniers on antique surveying instruments. But one scale that has always been a mystery to me appears on the Chandlee family of compasses. Etched into the base of the compass is a two-sided scale. On the left side is a column labeled with a capital "L," and on the opposite side is a column labeled "T." The prominent location of this scale told me that it was important, but no one could tell me how it worked, or even its purpose.
One day a good friend helped me decipher the mystery. Although he is not a surveyor, he builds and repairs antique instruments. Together we determined that the scale relates to the survey perch or pole. The Chandlee compasses were used in the last part of the 18th century, which was during the transition between the common use of the English survey pole and the colonial use of Gunter links and chains. Each pole contained 25 links of a Gunter chain. The purpose of the scale was to convert between survey links and tenths of a survey pole.
On the scale, the "T" side lists the numbers 1-10 and the "L" side lists the number of links in each tenth of a pole. So 2.5 links is equal to each tenth of a pole; 17.5 links is equal to seven-tenths of a pole, and 22.5 links is equal to nine-tenths of a pole. Twenty-five links equals one pole or perch. In essence, this scale was just a little field shortcut for the owner of the compass.
The Chandlee compass also has a tally counter that records in pole per mile and as well as chains, whereas later compasses keep the tally count in chains per mile. Much to my surprise, I recently found a copy of General Land Office (GLO) notes that keeps the count in poles per mile, not the usual 80 chains per mile.