15 digits is about the precision hand-held calculators provide, right? Many early NASA missions took HP calculators along in missions with trajectory routines in case the computer failed.
Hand-held calculators might have been carried on many NASA missions, but not the early ones. The first missions started in 1961 and hand-held HP calculators weren't invented until more than ten years later. By that time we had already been to the moon 6 or 7 times.
The first actual hand-held calculator I every saw was a Bowman Brain (simple 4 function calculator) it was for sale in 1971 at the MIT COOP (the bookstore). I only knew one person that bought one; the rest of us continued carrying around our slide rules (they came in handy leather holsters with belt loops.) The HP that came out about a year later was a real scientific calculator.
Years before that, sometime between 1965 and 1968, on an episode of Lost in Space (a TV program with a family of early space explorers lost in outer space) the son, Will Robinson, was carrying around a large device about 3 inches thick and a foot tall that looked like a calculator. I thought the idea quite marvelous and went to bed thinking about it and how much better it would be than my slide rule for playing around with calculations. (I was a weird kid.)
We must be about the same age. I went through college with a leather holster for my slide rule. I saw the first TI calculator after graduating from college in '71. I lusted after it and later I went to work at HP and got an HP. I was a super-fan of reverse-polish at that time. HP stayed with RPN for some time.
I spoke at some length with Fred Haise Jr, Lunar Module pilot of Apollo 13, and when I showed him my slide rule, he enthusiastically took it and started to play with it. Yes, astronauts used to use slide rules.
He asked me what I used to lubricate it, and showed some simple calculations to our host. He said he'd mostly forgotten how to use it, but it was clear that it was very, very familiar to him.
He signed it. Later I got Jim Lovell to sign it as well. One of my most treasured possessions. I only wish I'd had the presence of mind to get TK Mattingly to have signed it when I met him a year earlier. There is yet time.
The other side from the vector adder ("front" side at https://upload.wikimedia.org/wikipedia/commons/c/c4/StudentE... ) includes a circular slide rule with perfectly normal log scales for fuel, time, distance calculations, an extra scale to help with hours/minutes conversions, and some marks for various conversion factors, including lb/gal fuel and lb/gal oil for use in weight/balance.
The main difference between a straight and circular rule is that it has only one appearance of the index, so you don't have to move the slide around as much, and it's round so the equivalent of a 10" rule has around 3" diameter.
It also has other scales for converting altimeter/airspeed (really pressure gauge) readings into other numbers more useful for certain purposes like true altitude (good for missing obstructions) and "density altitude" (for estimating takeoff performance, also helpful for missing obstructions).
This is amazing. The idea of converting units of multiple types in a hurry when it matters with a slide or circular rule in imperial units is terrifying. Somehow doing that in metric seems less so, but the fact that the system got people to the moon relatively recently is still amazing.
BTW, the computers in the ship were also made by HP.
There is a great story about an incident where a waste recycling problem caused a mission to be aborted. There was urine all over the inside of the capsule. NASA publicly reported that it was a computer failure.
Unfortunately HP had just done an ad campaign about their computers in space. HP sued and NASA settled for an unknown amount.
The flight computers on any manned NASA spacecraft have not been made by HP. The Gemini capsules and the Space Shuttle used IBM computers [1,2] and Apollo used computers made by MIT (primary computers) and TRW (Abort Guidance System) [3]. I could also not find any information on a mission that failed in such a way.
Handheld calculators typically get between 8 and 12 digits of precision. A four-function calculator will top out at 8; a scientific calculator will offer more (plus scientific notation support).
15 digits is about what's offered in double precision floating point calculations.
The first actual hand-held calculator I every saw was a Bowman Brain (simple 4 function calculator) it was for sale in 1971 at the MIT COOP (the bookstore). I only knew one person that bought one; the rest of us continued carrying around our slide rules (they came in handy leather holsters with belt loops.) The HP that came out about a year later was a real scientific calculator.
Years before that, sometime between 1965 and 1968, on an episode of Lost in Space (a TV program with a family of early space explorers lost in outer space) the son, Will Robinson, was carrying around a large device about 3 inches thick and a foot tall that looked like a calculator. I thought the idea quite marvelous and went to bed thinking about it and how much better it would be than my slide rule for playing around with calculations. (I was a weird kid.)