Dating K&E Slide Rules

Dating a particular K&E slide rule can be a challenge. In most cases dating of a particular slide rule requires consideration of several parameters. The following characteristics are used in combination with each other to fully identify a given rule:


Model Numbers:

 

Serial Numbers:

Serial numbers started in 1922 beginning with 0 and going through 999,999 then rolling over to 0 again. There were three rollovers occurring in 1945, 1955, and 1968. The following graph approximates the four production cycles.

 

Dates Marked With Stars: The stars in the above chart represent benchmark dates for particular rules where their purchase dates are known. Rules are only accepted as benchmarks if they were main sellers and usually did not sit on distributors shelves very long.

Benchmark Rules: (Follow links for details)

It should be noted that the production rate changes at some of these benchmarks. At this time we do not have enough benchmark rules to allow approximating a smooth curve. It is obvious that the production rates did not change at these dates exactly. Even though the approximations that are implied by this chart are a bit rough they probably fit in the +/- one year accuracy category.

If you have a K&E rule with a serial number that you know its purchase date, it would be greatly appreciated if you would let me know the details of it.

clarkmccoy2@comcast.net

The Start Date for Serial Numbers: The 1922 start date for serial numbers is based on a particular rule in my collection. It is a 4092-3 with the early scale set. It has an early serial number, 8041. The 4092-3 was first mentioned in the 1922 Slide Rule only catalog and this rule does not have laminated edges as later rules do. This rule also has the production numbers stamped on the ends of the frame like earlier rules. This rule is definitely from a production transition time which coincides with the 1922 4092-3 introduction.

Use of Serial Numbers In Collecting: Serial numbers can be used to approximate the manufacture date of a given rule however not necessarily the sales date. The common rules were produced in regular batches but the specialty rules did not sell as well and a given batch of rules might stretch over several years. It is not uncommon to find rules in the 1960s in 68 xxxx series packaging but 4000 series model numbers on the rules. Because the 68 xxxx model numbers started at about serial number 550,000 it is safe to say any 68 xxxx model number rule with a serial number lower than 550,000 would necessarily be in the fourth series of serial numbers produced after 1967.

Exceptions To The Serial Number Sequence: The serial number sequence that is described here only applies to wood framed rules from 1922 on. The following are exceptions to the serial number sequence:

Serial Number Placement: On early rules the serial numbers were usually on the rule in two places, the end of the slide and the bottom edge of the frame. The presence of two serial numbers on a given rule was to facilitate manufacturing allowing the mating of pieces of rules in final assembly. The slides and frame were cut from the same piece of stock and for best stability over the life of the rule they should be mated together in final assembly. From the early 1950s on the serial number is on the slide and the last three digits of the number is repeated on the frame pieces to facilitate mating of the parts.

Use of Serial Numbers at K&E: Because these numbers are not unique there has been some controversy in the collecting community over calling these numbers, "serial numbers". To help resolve this question I contacted Joe Soper about how these numbers were used at the Salisbury plant that he supervised for K&E. They called them "serial numbers" in the work environment. Their use of the numbers was to track production batches incase there ever were a complaint in the field about a workmanship problem. The numbers were also used when a bin of rule parts was dropped and the rule parts sets needed to reassembled. If this was their only use of the serial numbers then there was never a need to look back for more than three to four years. They had a forever warranty so serial numbers were not used for warranty qualification. A serial number rollover ever ten years or so did not pose a problem. They certainly did not care about collectors 50 to 80 years later trying to make sense of them.

Detail Charts of Serial Numbers: The following charts approximates the serial number ranges for each year from 1922 until 1976. These approximations should be accurate within +/- one year. If you observe a clear error in these charts please contact me. In discussions on particular slide variants in this site, portions of these charts will be used to identify the start of particular variants.

The yearly production rates shown in these charts are interesting. In general the increase in these rates shows an increase from 1922 that peaks in the early 1960s. The decline in the numbers from the early 1960s on probably can be attributed to these numbers not reflecting the sales of plastic slide rules. In the 1960s the sum of all slide rules sold is probably more like 150K/yr.

It should also be noted that K&E did not have serious competition in the US until the 1950s when Pickett, Post, and Dietzgen definitely took a share of the market. By the late 1950s Pickett reported sales of 100K/yr. Several different K&E executives have said that K&E did not make money on the wood framed rules and they were only kept in the line for the prestige they brought. Between their insane QC standards and their forever warranty that statement is probably true. It is reported that their plastic slides rule did make money because of their lower production costs.

  SERIES #1     SERIES #2  
Year Begin End Rate/Yr Year Begin End Rate/Yr
1922 0 37,000 37,000 1944 0 77,000 77,000
1923 37,000 74,000 37,000 1945 77,000 154,000 77,000
1924 74,000 111,000 37,000 1946 154,000 231,000 77,000
1925 111,000 148,000 37,000 1947 231,000 308,000 77,000
1926 148,000 185,000 37,000 1948 308,000 385,000 77,000
1927 185,000 222,000 37,000 1949 385,000 462,000 77,000
1928 222,000 259,000 37,000 1950 462,000 539,000 77,000
1929 259,000 296,000 37,000 1951 539,000 616,000 77,000
1930 296,000 333,000 37,000 1952 616,000 693,000 77,000
1931 333,000 370,000 37,000 1953 693,000 770,000 77,000
1932 370,000 407,000 37,000 1954 770,000 847,000 77,000
1933 407,000 444,000 37,000 1955 847,000 924,000 77,000
1934 444,000 481,000 37,000 1955 924,000 1,000,000 77,000
1935 481,000 518,000 37,000
1936 518,000 578,000 60,000
1937 578,000 638,000 60,000
1938 638,000 698,000 60,000
1939 698,000 758,000 60,000
1940 758,000 818,000 60,000
1941 818,000 878,000 60,000
1942 878,000 938,000 60,000
1943 938,000 1,000,000 60,000
  SERIES #3     SERIES #4  
Year Begin End Rate/Yr Year Begin End Rate/Yr
1956 0 88,500 88,500 1967 0 60,000 60,000
1957 88,500 177,000 88,500 1968 60,000 120,000 60,000
1958 177,000 265,500 88,500 1969 120,000 180,000 60,000
1959 265,500 354,000 88,500 1970 180,000 240,000 60,000
1960 354,000 442,500 88,500 1971 240,000 300,000 60,000
1961 442,500 542,500 100,000 1972 300,000 360,000 60,000
1962 542,500 642,500 100,000 1973 360,000 420,000 60,000
1963 642,500 742,500 100,000 1974 420,000 480,000 60,000
1964 742,500 842,500 100,000 1975 480,000 540,000 60,000
1965 842,500 916,500 74,000
1966 916,500 990,500 74,000

 

Catalog Descriptions:

Full line K&E catalogs were produced every five to six years except in the early 1900s where it was about every three years. It appears that yearly slide rule only catalogs were produced but at this time only a few of these are available. There were also Educational Products catalogs that contained slide rules.

Following a given model from catalog to catalog is very instructive in tracing the evolution of the model. A date range for a given model can be established doing this. Many of the major variations of a given model can be observed and thereby putting a date range on that variant.

Care must be taken in assuming that a particular model was carried between any two full line catalogs. There are cases of entire models coming and going between full line catalog issues. There are slide rule model numbers that never appeared in any of the full line catalogs. There are other models that never appeared in any catalog.

There are mistakes in the catalogs both in descriptions and illustrations. Many of these are subtle and usually do not make much difference.

In the 1930s and 1940s some of the illustrations show serial numbers on the rules. Some people think these numbers have significance. If they do it probably is limited to being that it might have been a real serial number at the time the illustration was drawn. Many of these illustrations were used over and over in many catalogs and obviously the serial numbers did change in that time frame.

 

Production Changes:

K&E continually upgraded their production methods and styles. In general it is safe to say that when a major change was done it was done to the whole line of slide rules. The dates of these changes therefore are benchmarks in time to compare rules to.

The presence of a given cursor on a rule can sometimes be misleading. Replacement cursors were sold for all previous models.

 

Patent and Copyright Dates:

Patent and copyright dates are often quoted by sellers of slide rules implying that the rule is that old. The date of a patent only means that the rule was not produced before that date.

It is very common to see 4053-3s for sale quoting the 1900 patent date. The first production of the 4053-3 was in 1913. The 1900 patent date shows up on all 4053-3s until the beginning 1930s. The 1900 patent was for generic construction techniques used on all Mannheim type rules. It is common to see 4053-3s on eBay with a 1934 style cursor and seller declares it was produced in 1900 because of the patent date on it.

Copyright dates in instruction manuals suffer from the same problem as patent dates. Very often it is necessary to do a page for page comparison of two manuals with different copyright dates to find out if there is a difference. Manuals before 1920 are poorly organized and often contain instructions for several types of rules.

 

Variants:

K&E slide rules evolved continually. On a given rule you will find that scale sets, model numbers, construction methods, printing styles, packaging, and logos evolved. I believe that in the early years, 1900 to 1930, that there maybe slight changes in almost every production run.

A particular family of rules such as the 4088 gained members and lost some over its life span. Some of the variants are visible in catalogs, others are not. Knowing the existence of these variants can help in identifying a particular rule.

Understanding this subject has been the drive behind this website. For the avid K&E collector these variants are a nightmare and a blessing at the same time. The collecting will never end. The puzzle will never be completed. There is always another rule to look for.

Example: 4053 Family of slide rules

The 4053 first appeared in the 1909 catalog as just a 10" rule with no dash number. The dash number scheme for designating length was introduced in 1913. The 4053 and 4088 families were the first use of the dash number scheme. A 5" plastic version of the 4053 is listed in the 1972 catalog showing how long the family of rules lasted. The following is a brief history of the 4053 family of slide rules as is told in the K&E catalogs that are available at this time. Exact timing is not possible because of the time between catalogs.

Each of the major family groups of slide rules have similar stories. The 4080/4081/4083 families have a very fascinating series of variants.