Hemmi Slide Rule Catalogue Raisonne
Determining Dates of Hemmi Slide Rules
Jirou Hemmi and Co. was founded in
1895 but no Hemmi slide rules from before about 1913 are known. Hemmi
was granted Japanese patent 22129 in 1912 for laminated bamboo construction
and success seems to have followed quickly thereafter. Tamaya and
Co. in Tokyo started selling Hemmi slide rules in 1913 as did the Hughes-Owens
company of Canada in 1914. The Frederick Post Company of Chicago began
selling Hemmi slide rules exclusively in 1931.
One can estimate dates of Hemmi slide
rules from markings on the rules.
| Before 1928 |  Signed
by “J. Hemmi,” not “Hemmi.” |
| 1927/32 | Hemmi introduced a new model numbering system between 1927 and 1932. (I have not been able to narrow the date.) Rules with model numbers 1-18 date from before this changeover, rules with model numbers 20 and above were made after the changeover. EXCEPTIONS: Hemmi continued offering models 1, 5 and 8 to its distributors until WWII or later; these rules occasionally turn up with Post or Hughes-Owens model numbers but no Hemmi model number. |
| 1928 -1946 |  The
company was reincorporated and name was changed from "J. Hemmi and Co"
to "Hemmi Keisanjaku" in 1928. Brand name is “Hemmi” (not “J. Hemmi”)
and “SUN” is in quotation marks. |
| 1937-40? |  The
first inch or first five centimeters of the measuring scales on ten-inch
closed body rules is extra-finely divided. Although discontinued
about WWII on ten inch rules; a short section of extra fine divisions continued
until the end of production on models 86K and 86/3K. |
| 1946 -1951 |  No
quotes around SUN, marked “Made in Occupied Japan.”
The United States occupation of Japan lasted from August 1945 until April 28, 1952. However, it is unlikely that Hemmi produced many slide rules during reconstruction in 1945 and no "Occupied Japan" rules are known with date codes. Therefore it is not unreasonable to assume that "Occupied Japan" rules date from 1946 or later but before Hemmi date coding became common in late 1951. |
| WWII-1955 |  From
WWII until 1955, Hemmi "Mannheim" slide rule models 30, 32, 34R, 34RK,
50 and 50W had S (sine) scales that ran from 5o44' to 90o
and were keyed to the C and D scales. Note the S scale on the upper
slide in the illustration. Before WWII and after 1955
the S scale ran from 34' to 90o and was keyed to the A and B
scales. The S scale on the lower slide in the illustration
is an example. Both slides are from Hemmi model 50W slide rules;
the upper from a rule dated September 1952; the lower from a 50W dated
May 1965. |
| 1950-1952 |  No
quotes around SUN, no date code. |
| 1951-1975 | 
There is a small date code in the form “YM” engraved into each slide rule
but often not colored. First letter is year of manufacture with A
= 1950. Second letter is month with A = January. Thus “BB”
indicates February 1951. All-plastic rules use the same date codes
preceded by “^” so that the date code looks like “^YM.”
“A” date codes are rare; the only rule I know of with an "A" date code is a model 86/3K with an "AL" (Dec 1950) date code. Most rules from 1950-52 escaped dating. The latest date code I'm aware of is "ZB" (Feb 1975) on a Hemmi 254WN owned by Warren Salomon. Ted Hume and I were the original decypherers of the Hemmi date code system; we published it in the Fall 2000 issue of Journal of The Oughtred Society. |
| 1974-1976 | The date coding system ran out with “Z” in 1975 but the application of date codes seems to have been erratic for a few years before then. Hemmi stopped making slide rules about 1976. |
The date code reveals the date of most
post-1950 Hemmi slide rules but it is not absolutely reliable. Some
Hemmi slide rules that clearly should have date codes, don’t. A very
few have two different date codes; a few have date codes that are as much
as five years earlier than the slide rule model was known to be made.
(I speculate that the date code represents the date of the blank—not the
date that the rule was engraved.)
Cursors
Cursors are not reliable indicators of the age of slide rules; too many broken cursors were replaced with newer models. That having been said, it would be foolish to ignore the cursor when estimating the age of a slide rule. Here are scans of some Hemmi cursors with information about their ages.Unmarked Cursors
The Hemmi cursors shown here carry no brand or maker's identification. Tom Dilatush has compared one to several old Faber cursors and is of the opinion that the design was copied from Faber.
Cursor B is unpolished soft aluminum. The plain version (non magnifying, non decimal-indicating) appears only in the 1913 Tamaya catalog. Magnifiying and decimal-indicating versions (but not plain versions) appear in the 1914 Hughes-Owens and the 1919 Tamaya catalogs.
Cursor C is unpolished soft aluminum and essentially identical to B except that the frame around the glass is narrower and the inside frame corners are not rounded. The plain version first appeared in the 1914 Hughes Owens catalog and magnifying and decimal-indicating versions first appeared in the 1919 Tamaya catalog (in which some rules were still shown with magnifying and decimal-indicating versions of cursor B). Available in standard, magnifying, decimal-indicating, and magnifying-decimal-indicating versions.
Cursor D is the "decimal-indicating"
variant of C. Hemmi's 1912 patent application shows this style cursor.
Cursors Marked "J. Hemmi"
Cursor B is "frameless" glass, also patent 51788. ("Made in Japan" has been removed from the specimen shown.) Hemmi referred to it as the "Type B" cursor. It first appeared in the 1926 Hemmi catalog and had vanished from Hemmi material by 1936. A magnifying version was available.
Cursor C is Hemmi's famous "Type A"--patent 58115--cursor. Construction is polished aluminum. Available in standard, magnifying, decimal-indicating, and magnifying-decimal-indicating versions. Type A was Hemmi's top of the line cursor from 1925 to WWII.
An interesting variant of the type A
cursor is the "extended magnifying lens" cursor from 1926-27. None
is known to have survived.
Cursors Marked "Hemmi"
Company name was changed from "J. Hemmi" to "Hemmi" in 1928.
Illustration C shows Hemmi's Improved
Type A cursor with a narrow chrome-plated frame. This improved type
A cursor was introduced about 1934 on Hemmi's less sophisticated rules
and gradually supplanted the type A cursor on other rules, completely replacing
it around WWII. Dates: 1934-end of production.
Type
A Cursors Marked Only "SUN"
Some Hemmi type A cursors are marked only
"SUN" with neither "J. Hemmi" nor "Hemmi" as manufacturer. In some
cases, as in the cursor shown here, that may be because there was not enough
room on the cursor to include the manufacturer's name but I have many full-size
type A "SUN" cursors with ample room that carry no manufacturer's name.
The cursors so marked seem to span the whole lifetime of type A cursors
from1925 to WWII.
Cursors Marked "Made in Occupied Japan"
The American occupation of Japan lasted from 1945 until 1952 but Hemmi slide rules and cursors were marked "Made in Occupied Japan" only from 1945 to sometime in 1951. All Hemmi closed-body rules used improved type A cursors during this period.
All-Plastic
Cursors
About 1927-28, all-plastic models 24 and
34 carried celluloid cursors; they are the only all-plastic cursors I know
of before WWII.
Hemmi re-introduced all-plastic cursors
on its less sophisticated rules in the 1960s. There is a wide variety,
ranging from small cursors with high magnification to elaborate, multi-line
cursors. These cursors are too varied to be described by any
general principles but their slide rules usually carry date codes.
Duplex
Cursors
All ten- and twenty-inch Hemmi bamboo
duplex slide rules used chrome-framed glass cursors like those shown in
the illustration at right. The design on the left was used on 1-3/16-inch-
and 1-5/8-inch-wide rules from their introduction c1930 until about 1955.
The design on the right was used on all 1-3/4-inch wide duplex bamboo rules
of any date (c1950 until end of production) and on 1-5/8-inch-wide rules
after c1955.
All Hemmi five-inch bamboo duplex
rules use chrome-framed glass cursors like this.
Hemmi
plastic
duplex slide rules used all-plastic cursors like those shown in the illustration
at right. The design on the left was used on extra-thick (about 5mm)
duplex rules. The design on the right was used on thinner (4mm) rules.
Patent and Other Dates
Here is a list of dates which may be useful: Rules which are imprinted with a patent number cannot have been made before the patent was issued but there is no limit to how many years after the patent date the rule was made. The absence of a patent number provides no information about the date of manufacture; slide rules intended for sale in Japan never carried US or British patent numbers--no matter when they were made.| 1895 | "Hemmi Jirou & Co." founded. Rules were marked "J. Hemmi" or "Tamaya" (Hemmi's first retailer). |
| 5/11/12 | Japanese Patent 22129 for Laminated bamboo construction. |
| 1917 | British Patent 107562 for laminated bamboo construction. |
| 4/5/20 | Japanese Pat. 51788 for method of attaching glass to cursor. Initially used on metal-framed cursors; later on frameless ("Type B"). (Date thanks to Clay Castleberry and Atsushi Tomozawa.) |
| 2/3/20 | US Patent 1329902 for laminated bamboo construction. |
| ca 1921 | Japanese Patent 58115 ("Type A" cursor). |
| 1921 | US import marking requirement changes from "Japan" to "Made in Japan" (but not consistently enforced until ca 1925). |
| 1925 | Pythagorean scales, P & Q introduced. |
| ca 1927 | Model numbering system revised. Models 1-18 dissapear; model numbers above 20 introduced. |
| 1928 | Company renamed "Hemmi Seisakusho & Co." Rules are marked just "Hemmi," no longer "J. Hemmi." |
| 1929-45 | "SUN" in quotes. |
| 1931 | Gudermanian scale, Gtheta, introduced. |
| 5/4/37 | US Patent 2079464 for Gudermanian/hyperbolic scale. |
| 1946 | Company renamed "Hemmi Keisanjaku Co." |
| 1945-50 | Rules marked "Made in Occupied Japan." |
| 1950 | Date codes introduced. |