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I bought this watch in the mid 80s, and used it for a few years for various sundry engineering calculations. Then it sat in a desk drawer for a long time, until I recently got it out and started playing with it. The battery was missing, but a CR2016 seems to work ok in it (I've learned that it originally used a CR2020, which sounds familiar, and is a hair thicker than the 2016). The watch still works fine, the calculator works fine, although the alarm contact spring is messed up and doesn't work. I don't like beeping watches, anyways, so that's not a problem. I discovered that setting the date requires telling it that we're in the 21st century now; if I set it to YYMMDD then it assumes the year is 19YY, but if I set it to YYYYMMDD then it works properly. Who'd have thunk these things would be worth several hundred bucks after all these years? I guess that's why they're called collector items.
Hewlett Packard HP-11C Calculator
I got this calculator as a gift at the end of 1981. I used it
the last two years of college, and since then at home as the need arose...which
was not very often.I've had to change the batteries a couple times, and
I found another 11c at the thrift store recently for a dollar, which the
kids get to use now.
In the 1880s, there
was a need for a reliable adding machine. Door E Felt invented one, which
he produced as the Comptometer. There were quite a few made, including
my example. This one has a most recent patent date of November 2, 1920,
and a serial number of 226,158. It can add, subtract, multiply, and divide!
You can use it to do percentages, and many other things. It operates as
a mechanical base 10 abacus. Pushing the keys adds that amount to the numbers
displayed in the little windows at the front. The lever on the right clears
the total. To add, you simply press in the first number, then the second,
then the third, etc. Read the total, then clear the machine. To multiply,
you enter one multiplicand repeatedly, the number of times of the last
digit of the second multiplicand. Then, move the fingers to the left one
space, and enter the first number again repeatedly, the number of the next
higher digit of the second multiplicand. Continue the process till you
have finished the second multiplicand. The little numbers by the windows
can be swung up to indicate where the decimal would be. Subtraction involves
adding the 10s complement, then subtracting one. The small numbers on the
keys are used for subtracting, and the little buttons just in front of
the first row of keys are used to keep the most significant digit from
carrying. Division requires subtracting repeatedly.