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This 21R
was made in Mexico, rather than at the Portsmouth factory (though examples were&mdashsee
here),
and is a basic four function model with an added percent and memory.
Note that, compared to the 8R or
18F, the equals
key is moved to a more 'modern' position. I believe that the 21R is
a 20R with rechargeable batteries and charger included (an accessory
kit was available as a model 01R---in the U.S. at least). The markings
are also different, with the memory M+, M- etc. missing from the 20R.
This model was marketed as 'The Answer', whereas some other of the Rockwell
calculators are marked as 'Slide Rule'. I'm unsure which came first, or whether
'The Answer' was solely for the U.S. market. The front of the box
for this calculator is shown on the right. The logo 'The Answer' is
only printed on the sides. I have also seen examples where
'memory' and '21R' are printed on the keyboard face (on this model
they are hidden, being on the bottom end of the keyboard).
This example has its I.C. labelled 7524 (1975 week 24). The manual for the 21R is available on the manuals page.
Try it out---it works!