How did the pioneer ‘odometer’ work?

    “How did the pioneer ‘odometer’ work?” Ensign, Aug. 1981, 30–31

    On page 31 of the Gospel Doctrine manual My Kingdom Shall Roll Forth is a picture of a pioneer “odometer.” How did it work, and how was it connected to the pioneer wagons?

    Norman E. Wright, professor of Computer Science, Brigham Young University. The wooden odometer designed, built, and used by the first company of LDS pioneers in 1847 has a brief but fascinating history. Personal journals of members of that company provide many insights into the circumstances surrounding its development and use; they also contain detailed descriptions of the machine as it was originally proposed and finally built and used.

    The three brethren principally involved in the odometer project were Orson Pratt, William Clayton, and Appleton Harmon. Just ten days and seventy-five miles out of Winter Quarters, Brother Clayton recorded in his journal:

    “I walked this afternoon in company with Orson Pratt and suggested to him the idea of fixing a set of wooden cog wheels to the hub of a wagon wheel in such order as to tell the exact number of miles we travel each day. He seemed to agree with me that it could be easily done at a trifling expense.”1

    Brother Clayton was dissatisfied with simply guessing how many miles were traveled. He tells us that his estimates were consistently two to four miles less than those of the other brethren, and he was anxious to know “the exact number.” Then, too, he was compiling data about the journey: route, terrain, conditions along the trail—water, grass, timber—and of course, the distances between prominent landmarks and campsites. Such information would be near useless if the mileages were not precisely correct.

    A few weeks following his conversation with Orson Pratt, Brother Clayton measured the left rear wheel of one of Elder Heber C. Kimball’s wagons and found it to be ideal for his purpose. It was 4 feet 8 inches in diameter, hence 14 feet 8 inches in circumference. Three hundred and sixty rotations of this wheel equaled a mile exactly, “not varying one fraction.”

    On 8 May 1847, near the site of present-day North Platte, Nebraska, Brother Clayton tied a marker on the spoke of his measured wheel (some sources say it was a piece of red flannel) and walked beside it all day long, tallying each rotation. He tells us frankly that the method was “somewhat tedious.” At the end of the day he had tallied 4,070 rotations. For the first time, he knew the exact distance they had traveled: “eleven and a quarter miles—twenty revolutions over.” It must have been with considerable satisfaction he learned that his “exact number” was two miles under the estimates others gave for the same day’s travel.

    Two days later, Orson Pratt discussed Brother Clayton’s suggestion with President Brigham Young; then, with the President’s approval, he spent the afternoon working on its design.2 The machine he proposed used the principle of the “endless screw” or worm gear—a threaded rod set into the teeth of a gear wheel (see figure, A). As the rod makes one complete revolution, the threads pull one tooth of the gear wheel the distance from one tooth to the next. If the wheel were to contain sixty teeth and the rod were to rotate only once for every six turns of the wagon wheel, then 360 revolutions of the wagon wheel would produce one complete gear-wheel rotation. This, of course, is one mile exactly if Clayton’s measured wheel were used as the input driver to the mechanism.

    The next step in the gear chain proposed by Brother Pratt involved another endless screw at a right angle to the first. Since this feature was difficult to build and install correctly, it appeared on the machine that was built in a modified form.

    Once the project was under way, it did not take long to complete. Appleton Harmon, a skilled carpenter and mechanic from Nauvoo, was assigned the task of constructing the machine. He began work immediately, and six days later, 16 May 1847, the odometer was installed and operating.

    The only description we have of the completed odometer is in William Clayton’s journal.3 He wrote: “About noon today Brother Appleton Harmon completed the machinery on the wagon called a ‘roadometer.’ … We are now prepared to tell accurately the distance we travel from day to day which will supercede the idea of guessing and be a satisfaction not only to this camp, but to all who hereafter travel this way.”

    Using the accompanying diagram as an aid, let me paraphrase his description of the odometer: As the measured wagon wheel turns, a cog on its rotating wheel hub strikes one of the projecting arms of the mechanism’s drive rod. Six turns of the wagon wheel produce one complete rotation of this rod (see figure, B). With each rotation of the rod, the threads at its upper end draw by one tooth of the 60-tooth gear wheel. One complete rotation of this wheel, therefore, represents 360 (6 times 60) rotations of the wagon wheel, or one mile.

    The axle of the 60-tooth gear wheel has 4 cogs cut into it. These work on a second gear wheel of 40 teeth (see figure, C). With every rotation of the 60-tooth wheel, four teeth of the 40-tooth wheel will be drawn by, each representing a quarter of a mile. One complete rotation of the 40-tooth wheel, therefore, represents ten miles. If the day’s journey were more than ten miles, the odometer would pass through its initial position for that day and continue rotating.4

    The fact that the whole mechanism was encased in a protective box, 15 by 18 by 3 inches, gives us some idea of the size of the gear wheels. To fit within those dimensions, they could not have been larger than 10 inches in diameter and not more than 1 inch thick.

    But to know how the odometer worked is one thing; to know the detailed specifications of construction is quite another. This we cannot know, since the original odometer with its three moving parts is lost. I have searched for these items without success. It would be exciting indeed if these original pioneer artifacts could be found.

    The machine pictured on page 31 of the 1980 Gospel Doctrine manual, My Kingdom Shall Roll Forth, is indeed a pioneer odometer, but it is not the one made in 1847. It was built in 1876 by Thomas G. Lowe of Franklin, Idaho. Actually, the original pioneer odometer was not the first such device invented, although many published accounts have so stated. Odometers of various designs were in common use in the United States and in Europe at the time the pioneer machine was made.

    William Clayton’s odometer was successfully used by the first pioneer company in measuring the distance from western Nebraska to the Great Salt Lake Valley. On 17 August 1847 he joined a company making the return trip to Winter Quarters. He had received instructions from President Young to again measure the distances along the trail and make them available “for public benefit.” To do this, a new odometer was built which would count up to 1,000 miles—a 100-fold improvement in measuring capacity. This second machine was built by William A. King.

    Arriving at Winter Quarters on 21 November 1847, Brother Clayton wrote:

    “I have succeeded in measuring the whole distance from the City of the Great Salt Lake to this place, except a few miles between Horse Creek and the A La Bonte River which was taken from the measurement going up. I find the whole distance to be 1032 miles and am now prepared to make a complete travelers guide from here to the Great Salt Lake.”5

    In March of 1848, Brother Clayton published his Latter-day Saints’ Emigrants’ Guide. Because of its accuracy, it soon became one of the most respected guides of the day.

    1. William Clayton, William Clayton’s Journal (Salt Lake City: Deseret News, 1921), p. 83.

    2. Orson Pratt and others, Exodus of Modern Israel (Independence, Mo.: Zions Printing and Publishing, n.d.) p. 36.

    3. Clayton, pp. 152–53.

    4. It is probable that the distances traveled each day were calculated from differences in the relative positions of the two gear wheels on a continuous basis, rather than by resetting the machine to a “zero” position at the beginning of each day. To do this, the individual teeth would need to have been uniquely numbered or marked.

    5. Clayton, p. 376.