Measuring and Calibration

The International System of Units (SI) is the modern metric system used globally for precise measurement. It defines seven base units (meter, kilogram, second, ampere, kelvin, mole, and candela) from which all other units are derived. These units are universal, coherent, and based on fundamental physical constants. By adopting SI units, a post-collapse society can restore scientific progress, fair trade, and efficient resource management, laying the groundwork for sustainable development.

Useful Things to Note

Scientific Notation

Numbers can get large really fast. To shorten this so that we don't have 30 zeros floating at the end of every number, we use some basic math to describe a notation. If the number has a E(some number here), e(number), or even x10^(number), this stands in the place of x10^(number).

This means that you can shorten the number 467,110,000,000 to 4.67110000000x10^11 or, roughly 4.67E11. A negative number means the same that any negative exponent means. (See basic rules of Math)

This means you can turn the number 0.000000846 to 8.46E-7.

Prefixes

Because the previous notation can be hard to read, prefixes are available to whatever unit you want. For instance, instead of 2.53x10^-5 meters, you could say 25.3 µm which means 25.3 1 thousandths of a meter. This is much easier to picture even though it is still really small.

A common set of these prefixes go as follows:

name	symbol	meaning		name	symbol	meaning
queta	Q	x1030		quecto	q	x10-30
ronna	R	x1027		ronto	r	x10-27
yotta	Y	x1024		yocto	y	x10-24
zeta	Z	x1021		zepto	z	x10-21
exa	E	x1018		atto	a	x10-18
peta	P	x1015		femto	f	x10-15
tera	T	x1012		pico	p	x10-12
giga	G	x109		nano	n	x10-9
mega	M	x106		micro	μ	x10-6
kilo	k	x103		mili	m	x10-3
hecto	h	x102		centi	c	x10-2
deka	da	x101		deci	d	x10-1

Base Units

Time: the second (s)

The second is historically defined through the duration of the day. One day is divided into 24 hours, which are first divided into 60 minutes which are in turn divided into 60 second each.

• 1 day = 24 hours, 1 hour = 60 minutes, 1 minute = 60 seconds.

There's also a "human" way to track time, but it can differ on all sorts of elements. Take this as a basic way to tell time.

Methods to track time

Unit	How to measure	Equivalent to
Breath	Inhale and exhale.	~5 seconds
Heartbeat	Place your second and third finger from your thumb, on your wrist or neck, every beat is a pulse.	~1 second
Sunrise to sunset	From the moment you can see the sun, to the moment it can't be seen anymore.	~11-16 hours, depending on season and place
One sunrise to another sunrise	From one sunrise to another.	~1 day
30 sunrise to sunrise cycles	The time it takes to see 30 sunrises.	~1 month
One year	About every 12 months.	~365 days

More recently the second has been redefined as a number of vibrations of the cesium element, but in everyday life this definition does not have practical use.

Distance: the meter (m)

The meter is described to be roughly the length of a large walking step. Using the more precise definition of the distance light can travel in 1/(299,792,458) seconds. This comes out to be roughly 3.33564095E-9 seconds.

To approximate the meter, several methods exist:

1. A second-pendulum: by suspending a mass from a length of one meter and swinging it in small oscillations, the period of the pendulum is two seconds, which means it goes from one side to the other in one second.
2. A hand-based ruler: the length between the thumb and the pinky when the hand is fully extended is roughly 20cm. Therefore, five times this length is close to a meter.

Distance can be used to describe area, and volume, depending on the number of dimensions used:

• Two distances define an area, for example a one-meter by one-meter square has an area of one-meter-squared.
• Three distances define a volume, for example a one-meter by one-meter by one-meter cube has an area of one-meter-cubed.

Remarque: Yes, light has a speed, albeit incredibly fast. And as this speed is constant, it has been used to define the meter without requiring a physical object.

Mass: the kilogram (kg)

When the meter has been defined it can help to get the mass unit, the kilogram, which is defined as the mass of a volume of water in a 10cm x 10cm x 10cm cube.

Quantity: the mole (mol)

The mole is not really a unit as much as it is a big number which makes it easier to count bit quantities.

It is originally defined as the number of atoms contained in 12g of of carbon 12, now equal to exactly 6.02214076 × 10²³.

This number is huge and not really useful in everyday life and is mainly used in chemical processes which need precision.

Common derived units

Speed

Speed is defined as displacement over time, which gives it the unit "m/s" (Meter / Second)

The speed of light is defined to be exactly equal to 299,792,458 m/s

Acceleration

Acceleration is the rate at which speed changes over time: m/s/s (Meter / Second / Second), most commonly notated as m/s²

Frequency: the hertz (Hz)

One Hertz (Hz) is defined as 1/s, also notated as s^-1

Force: the netwon (N)

One Newton (N) is defined as the force needed to accelerate an object that has a mass of 1 kg at 1 m/s². A newton is kg×m/s²

Pressure: the pascal (Pa)

One Pascal (Pa) is the pressure that a force of 1 N exerts on a surface of 1 m₂

Energy: the joule (J)

One Joule (J) is the energy needed to displace a 1 kg object by 1 m using a force of 1 N. A joule is N×m