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An HP brochure from 1974 proclaimed "This man is holding the smallest
programmable computer ever".

In September 1975, an advertisement in Scientific American read:

    "HP-65 in space with Apollo-Soyuz.

    The American astronauts calculated critical course-correction maneuvers
on their HP-65 programmable hand-held during the rendezvous of the U.S. and
Russian spacecraft.

    Twenty-four minutes before the rendezvous in space, when the Apollo and
Soyuz were 12 miles apart, the American astronauts corrected their course to
place their spacecraft into the same orbit as the Russian craft. Twelve
minutes later, they made a second positioning maneuver just prior to
braking, and coasted in to linkup.

    In both cases, the Apollo astronauts made the course-correction
calculations on their HP-65. Had the on-board computer failed, the
spacecraft not being in communication with ground stations at the time, the
HP-65 would have been the only way to make all the critical calculations.
Using complex programs of nearly 1000 steps written by NASA scientists and
pre-recorded on magnetic program cards, the astronauts made the calculations
automatically, quickly, and with ten-digit accuracy.

    The HP-65 also served as a backup for Apollo's on-board computer for two
earlier maneuvers. Its answers provided a confidence-boosting double-check
on the coelliptic (85 mile) maneuver, and the terminal phase initiation (22
mile) maneuver, which placed Apollo on an intercept trajectory with the
Russian craft.

    Periodically throughout their joint mission, the Apollo astronauts also
used the HP-65 to calculate how to point a high-gain antenna precisely at an
orbiting satellite to assure the best possible ground communications.

    The first fully programmable hand-held calculator, the HP-65
automatically steps through lengthy or repetitive calculations. This
advanced instrument relieves the user of the need to remember and execute
the correct sequence of keystrokes, using programs recorded 100 steps at a
time on tiny magnetic cards. Each program consists of any combination of the
calculator's 51 key-stroke functions with branching, logical comparison, and
conditional skip instructions." 


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