## Hemmi
Model Numbers

Models
are listed in numerical sequence with slight re-arrangements to keep related
rules together. Model numbers beginning with P (e.g., “P40RK”) are
all-plastic. Other rules are celluloid over bamboo except as noted.

Model numbers that include
“/” followed by a digit (“80/3”) indicate the number of hairlines on the
cursor. For example, when Hemmi model 80 was first introduced in the
1920s it was simply “model 80” with a single hairline. But about 1932
Hemmi began supplying that slide rule in single- and triple-hairline versions
and the rules bore glued-on labels “80/1” or “80/3.” About 1951 a
K scale was added and the single-hairline version dropped from the catalog;
the surviving rule was model 80/3K--there was no single-hairline model 80/1K.
After another modification, the rule became model 80K with three hairlines
and no option of a single hairline.

In summary, a model number
like “80/3” indicates that the rule has three hairlines and tends to imply,
but does not guarantee, that there was also a single-hairline “80/1” model
available. A model number like “80K” gives no information about how
many hairlines are on the cursor.
The letter "A" added to
an existing model number indicates a change in bookkeeping without any
change in the slide rule itself. Model 90A is the same as model 90;
model 149A is the same as model 149. Other letters are mnemonic indicators
of the changes made--model 34RK is just model 34 with R and K scales added;
model 259D is the same as model 259 but with the scales rearranged and
a DI scale added.

Model numbers specify a
unique arrangement of calculating scales and length. Model numbers
did not change when the cursors were redesigned or over-range scale extensions
added or measuring scales rearranged. (For a discussion of measuring
scales on closed body Hemmi slide rules, click here.)
If you have a Hemmi slide rule with the same scale arrangement as a rule
shown here but with a different cursor, scale extensions, or measuring scales,
it's the same model.