Imagine that you are lying in bed. Now you are just waking up.
Your alarm clock woke you up.
It is a radio alarm clock.
It gets the time from PTB’s atomic clocks.
You get out of bed. You are still tired.
You would like to make a pot of coffee.
You pour water into the coffee machine.
You measured the right amount of water before that.
Your coffee is brewing now. You want to get dressed.
Is your thin sweater warm enough for today? You take a look at the thermometer.
It shows the temperature.
Every measurement device measures things in measurement units.
For example, time is measured using a clock.
The unit is called “second”.
Temperatures are measured using a thermometer.
The unit is called “degree Celsius”.
We often don’t notice the measurements at all.
A water meter, for example, measures how much water we use.
An electricity meter measures how much electricity we use.
And a gas meter measures how much gas a heating system uses.
PTB makes sure that measurement devices measure accurately and reliably.
Otherwise it would be a mess.