# How do you define speed in space?

Discussion in 'Hangar Talk' started by cowman, Jan 22, 2020.

1. ### Sac ArrowTouchdown! Greaser!

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I supposed it would be akin to wondering if it was lunch or dinner that is blowing out your rectum.

2. ### jim.nelsonPre-Flight

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We learned in 1970s computer science that base e was the most efficient.

3. ### deonbPattern AltitudePoA Supporter

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Sure but that's only because 0x0C (10) is a round decimal number. My point was that 10 itself is not otherwise a very naturally occurring number. We don't often buy or use 5 or 10 of anything, unless it's something artificially constrained to fit in with decimal or metric. Our world is full of rectangles, not pentagons.

Coming to math, calculating something like 0xFF00 / 0x10 or 0xFF00 / 0x100 is as trivial in hex as 9900 /10 or 9900 /100 is in decimal. However, that's where simplicity ends with decimal, but not with hex:

Observe these:
0xFF00 / 0x2 = 0x7F80
0xFF00 / 0x4 = 0x3FC0
0xFF00 / 0x8 = 0x1FE0

Now you may be confused - how is that easier that saying in decimal:
9900/2 = 4950
9900/4 = 2475
9900/8 = 1237

The reason is direct base conversion:

0xFF00 can also be expressed as: 0b1111 1111 0000 0000
/2 removes one digit at the end: 0b0111 1111 1000 0000
/4 removes two digits at the end: 0b0011 1111 1100 0000
/8 removes three digits at the end: 0b0001 1111 1110 0000

When you do this everyday, the conversion back and forth between 4-digit binary and 1-digit hex happen instinctive in your head - you can see the one number as the other. (I can anyway, but it took me a decade. A child can learn this in a month). So taking 0b1111 1111 0000 0000 and shifting it by 1, 2 or 3 digits become:
0b0111 1111 1000 0000 = 7 F 8 0
0b0011 1111 1100 0000 = 3 F C 0
0b0001 1111 1110 0000 = 1 F E 0

So now, not only can you trivially divide by 0x10, you can ALSO trivially divide and multiply by 2, 4, 8, 16, 32, 64, 128 (and 256 of course but that's just 16^2 (0x100) so equivalent to decimal 10^2 (100)).

Decimal has a similar trivial divide by 10 but doesn't have this easy back-and-forth base conversion. Well, it can of course convert to base 5 and get the same properties, but base 5 is not interesting enough in nature to make it worth our while. Rectangles, not pentagons.

Of course with hex you lose your ability to trivially divide by 10, but we only like dividing by 10 because we chose 10 as our base. If it wasn't chosen as the base, it would be about as common to divide by 10 as it would be to divide by 14.

DaleB likes this.
4. ### GeorgeCEn-Route

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Use binary, then you only ever need seven birthday candles.

5. ### smvPre-takeoff checklist

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There are 10 types of people in the world. Those that understand binary and those that do not.

The metric system was created for those who cannot count higher than 10(base10) without taking off their shoes.

6. ### DaleBEn-Route

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Speak for yourself. I plan to live 10000000 years.

7. ### GeorgeCEn-Route

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Me too, it'll roll over to zero.