|Early Hemmi trademark. The "J' was officially
dropped in 1928.
|Trademark 1928 - 1946. The company name
was officially changed from "J. Hemmi and Co" to "Hemmi Seisakusho &
Co." (Hemmi Engineering Works Co.) in 1928 but company was referred to
as "Hemmi Seisakusho" at least as early as 1917. Hemmi was
incorporated as a public corporation 1933 with no change in name.
|MIOJ 1947 - 1949. The Allied Powers occupation
of Japan lasted from August 1945 until April 28, 1952 but the requirement
that export goods be marked "Made in Occupied Japan" was in effect only
from 20 February 1947 to 5 December 1949. (Thanks to Wataru Tsuchihira
who found the original orders in the Japanese National Library.)
|Trademark 1950 - 52. No quotes around SUN.
|Extra fine divisions on measuring scale 1937? -
40? The first inch or first five centimeters of the measuring scales
on the bottom edge of 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.
|Date codes 1951-1975. There is a small date
code in the form “YM” engraved into each slide rule but often not colored.
That can make it difficult to find. Often it is in the lower left
of the rear of the rule but can appear almost anywhere. It sometimes
takes inspection with a magnifier in raking light to find the code.
First letter of the date code indicates the year of manufacture with A = 1950. Second letter indicates 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; I know of only two rules so marked. (Both are model 86/3K rules marked "AL" (Dec 1950)). 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.
The date codes reveal 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 code.
|There are two common ways to lay out the S, sine,
scale on closed-body rules: In the "Rietz" layout, the S scale runs
from 5o40' to 90o and is keyed to the C and D scales
on the face of the rule. In the "Mannheim" layout the S scale runs from
0o34' to 90o and is keyed to the A and B scales.
Rather perversely, from WWII until 1955 Hemmi "Mannheim" slide rule models 30, 32, 34R, 34RK, 50 and 50W had "Rietz" (not "Mannheim") S scales. Note the S scale on the upper slide from a Hemmi 50W slide rule dated September 1952.
Before WWII and after 1955 Hemmi "Mannheim" rules had "Mannheim" S scales. The lower slide is from a 50W dated May 1965.
|Scale Labels and Over-Range Extensions:
Top picture: Early Hemmi closed-body rules had neither scale labels no over-range extensions. (The rule shown is a Hemmi model 60/1, estimated date 1927.)
Middle picture. Over-range extensions, but not scale labels, were gradually introduced. (The rule shown is a Hemmi model 60/1, estimated date 1935).
Bottom picture: Scale labels and over-range extensions became standard about WWII. (The rule shown is a Hemmi model 64T with a date code for June 1968.)
Click on image to enlarge.
|Hemmi increased the thickness of the
metal end brackets on their bamboo rules in the early 1960s. The
older, thinner brackets measure about 10.5 mm from the surface of one bracket
to the outside surface of the opposite bracket (not including heads of the
screws and rivets). The newer, thicker brackets measure about 12.0
mm from surface to opposite surface. The thicker brackets hold the
cursor slightly above any flat surface on which the rule is laid.
The extra thickness is not apparent to the naked eye and I have not been
able to produce a photograph that clearly shows the difference. Like
many Hemmi features, the date of implementation of this feature is hard
to pin down. No literature mentions it. All my 1.75-inch-wide
bamboo Hemmi rules with date codes "O" (1964) or later have thick brackets;
all those with date codes "M" (1962) or earlier have thin brackets.
The earliest 1.625-inch-wide bamboo rule I have with the thicker brackets is a model 250 from 1960 (Date code "K.") --about three years earlier than for 1.75-inch rules.