Slide rules of the stanley rule & level company and other American makers

Slide rules of the stanley rule & level company and other American makers

Wyman, Tom

In the mid-1800s American manufacturers of conventional measuring rules were the primary source of slide rules. The “modern” slide rule era in America, which lasted until the early 1970s, can be said to have begun in 1883 when United States-based Keuffel & Esser Company first offered slide rules to American buyers. At first, K&E slide rules were manufactured by the German and French companies, but within a few years ME began to manufacture its own slide rules. Gradually, manufacturers of the modern slide rules forced old-line slide rulemakers to abandon their boxwood and brass slide rules which had been a part of their product lines for some seventy-five years.

The History of Routledge-type Slide Rules

If an American architect or early-day engineer wanted a slide rule in the mid-1800s, his choice was, for the most part, limited to a few slide rules produced by companies making measuring rules. These so-called “Routledge-type” slide rules were typically two-foot, two-fold boxwood rules with a metal two-cycle logarithmic slide or “Gunter scale” in one arm working against a similar scale on the body of the rule. The twocycle log scale was necessary because the rules had no cursor. As a result, these slide rules had an effective length of 51/4 inches with correspondingly poor accuracy.

The hinged rule, with its two-foot, two-fold design, was described by Englishman Henry Coggeshall in the 1729 edition of his book The trt of Practical Measuring Easily Performed by a Two Foot Rule that Slides to a Foot. Since Coggeshall was particularly interested in timber measurements, he also devised the girt line to facilitate such calculations. Coggeshall’s hinged rule with a slide in one arm was the basis for the development in 1808 of the engineers’ slide rule by Joshua Routledge (1773-1829) of Bolton, England. English rulemakers quickly adopted the Routledge design and began producing rules of boxwood with brass hinges and slides. Rules were also produced in boxwood and German silver, but occasionally for the wellheeled customer or for making special presentation rules, ivory was substituted for boxwood.

It didn’t take long for American rulemakers to begin to copy the Routledge design and to include slide rules in their own product lines. These measuring rules, which doubled as slide rules, were available in the forms of carpenters’ and engineers’ slide rules. On the carpenters’ rule the scale below the slide, the girt line, was folded at 4 to facilitate the calculation of board feet in standing trees and logs. Instead of the girt line, the engineers’ rules had a one– cycle log scale below the slide for use in calculating squares and square roots. Also, hand-stamped on the body of the engineers’ rule below the slide was a series of tables, conversion factors, and pumping engine gauge points to assist in technical calculations.

Stanley’s Routledge-type Slide Rules

Among the early makers of Routledge-type slide rules in the United States were Belcher Brothers, New York (1821-1876), and C. A. Stearns & Co., Brattleboro, Vermont (1838-1863). Another was H. Chapin (1834) which merged with D. H. Stephens & Co (1854) in 1901. As early as 1835 Clark & Co. of Brattleboro, Vermont, was producing a two-foot, two-fold carpenters’ rule with a Gunter slide which had an unusual circular fluted hinge (Figure 1). Philip E. Stanley reports that by 1839 H. Chapin offered both engineers’ and carpenters’ slide rules. Over the years some fifteen companies are known to have offered Routledge-type slide rules (See Table I).

From the mid-1800s, the dominant American rulemaker was Stanley Rule & Level Company of New Britain, Connecticut. Thanks to Phil Stanley and his meticulous research, good information is available on the measuring and slide rules produced by that company. Information on other rulemakers operating in competition with Stanley is not nearly as comprehensive. These makers and their associated product lines represent fertile areas for future research and documentation.

The various Routledge-type slide rules offered by A. Stanley & Co. and its successor company, Stanley Rule & Level Co., over a sixty-year period are summarized in Table II. Over the years the company offered five carpenters’ slide rules and two engineers slide rules. Understandably, rules inscribed ‘A. Stanley & Co., New Britain, Conn.” which were offered from 1854 to 1857 are particularly hard to come by. Prior to 1900, when the market for the company’s carpenters’ and engineers’ slide rules was the greatest, Stanley offered some 160 different standard measuring rules in its catalogs. A number of these measuring rules were of limited interest to customers and were quickly discontinued, while others continued to be offered for over a hundred years. In addition to offering a wide variety of measuring rules through its catalogs, the company produced an unknown number of non-standard or special-purpose rules. These custom rules were for selected markets and individual buyers, and often were designed for special advertising purposes. “Sliding rules” with the so-called Gunter scale were but a small fraction of the company’s total output.

Some rules (notably Nos. 15 and 16 among the Stanley rules with a Gunter scale) were bound or edged with brass strips to strengthen the rule and to protect the edges from wear. Although more costly, bound rules were less apt to be damaged in tool boxes and on the job. As evidence of this, it is more difficult to find examples of unbound rules that do not show considerable wear and abuse.

Stanley’s “Jas. Hogg” Slide Rule

The only true rectilinear slide rule manufactured by Stanley Rule & Level that was not first and foremost a two-foot, two-fold measuring rule was the “Improved Slide Rule Arranged and Constructed by Jas. Hogg” (Figure 2). The Hogg slide rule never appeared in Stanley’s standard trade catalogs. This trim boxwood slide rule bound tipped in German silver (12 inches LOA, 11/16 inches wide, and 3/16 inches thick) was designed for use by technicians in textile trades. However, the only features that suggest this particular use are three small metal plugs located at 5.5, 10 and 11.4 on the C scale and labeled G, H, and K, respectively, to mark constants related to textile calculations. In some rules these are brass plugs, but on the rule described here they are German silver. Like other Routledge-type slide rules produced by Stanley, the Hogg rule had no cursor.

The Hogg slide rule described here is stamped “Pat. Applied For” and was produced in Lawrence, Massachusetts. Other James Hogg slide rules were produced in Lowell, Massachusetts, indicating that the maker changed locations during the period that Stanley offered his slide rule. Hogg’s 1887 instruction booklet for this slide rule includes, ‘A practical course of instruction in the calculations of machinery for the superintendent and overseer in the textile manufacture, with rules, calculations, and tables.” This includes a detailed discussion of the use of the slide rule in making calculations governing the adjustment and operation of looms and weaving equipment.

From the top of the Hogg rule downward there are eight scales, the first six of which are lettered A through F, but bearing no relation to lettered scales found later on conventional slide rules. The scales are precisely calibrated in contrast to scales normally found on Routledge-type slide rules. However, since the slide rule lacked a cursor, calculations had to be made using twocycle log scales on the body of the rule and on the upper edge of the slide resulting in the same limited accuracy of the Routledge-type rules.

On the reverse side of the slide rule are numerical tables similar to those found on Stanley’s two-foot, twofold engineers’ rules. The Hogg rule displayed here has gauge points for pumping engines while the Hogg rule produced in Lowell, Massachusetts, omitted those gauge points. The fact that such data was included at all suggests the rigid tradition associated with displaying it on an engineers’ rule even when the rule was designed for textile mill operators. There is at least one random error in the gauge points hand-stamped on the rule. Such errors were not unusual on such rules given the sustained attention required to hand-stamp individually the 168 numbers comprised of 501 separate digits that appear on the typical engineers’ rule.

The Hogg slide rule appeared sometime prior to 1886, about the time that K&E began to sell slide rules. The fact that this quality slide rule did not attract the attention of more buyers who were seeking a better rule for technical calculations may be attributed in part to the fact that the rule had no cursor at the time when the cursor was becoming more widely available. Moreover, Stanley did not promote the Hogg rule as a generic “new and improved” engineers’ slide rule. The rule was certainly less expensive to produce than two-foot, two-fold models. It can be assumed that had it appeared in Stanley catalogs instead of being produced and marketed exclusively as a specialized rule for the textile trades, the rule would have attracted more buyers with the result that it would have been more commonplace today.


During the last half of the nineteenth century, the makers of measuring rules were producing slide rules primarily for builders, tradesmen, and merchants. Those makers apparently never awakened to the fact that there was a growing demand for quality slide rules among engineers and technicians. Oriented as they were toward the production of shop and on-the-job tools, makers of measuring rules didn’t appreciate the potential of this developing, more technically oriented market. At the same time, it is doubtful that companies producing measuring rules had the in-house expertise to design slide rules to meet this specialized demand. This may serve, even today, as an object lesson for company managements which lock onto a particular product line without remaining alert for ways to adapt and diversify and accommodate new emerging markets.

By 1900 few customers, perhaps other than the occasional tradesman, wanted a two-foot, two-fold rule with a sliding Gunter scale. Thus, in 1915, Stanley phased out its line of engineers’ and carpenters’ slide rules. The new, more versatile and accurate slide rule with its cursor and easy to read scales had become the favorite of those in technical fields. Tool collectors and historians should not forget that the old Routledge-type boxwood and brass rules were among America’s first widely available slide rules and thus are an important element in the development of industrial America and in the history of the country’s calculating devices. As such they deserve greater attention and research.

Copyright Early American Industries Association Sep 2001

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