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 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.
