Take one liter of water at "room temperature" an aprox of 20 Celcuis degrees at one atmosfere pressure. Take a straight transparent tube of one centimeter inner thickness. Put the water in without spilling.
"The length of the path travelled by light in vacuum during a time interval of 1/299792458 of a second, where the second is defined by a hyperfine transition frequency of caesium."
This is the actual definition, but it's also pretty weird.
Take a really long rope and put one end on either pole of the Earth, and the other end on the equator. Use the shortest path, and make sure the rope is tight. No squiggles allowed! Chop that rope into exactly 10 000 000 equal parts. One of them is as long as a meter. Now you just need to find the right one.
Okay, so, right, okay. Um. In German schools (and probably some other countries...?), many many years ago (possibly still today? or maybe it's all digital now? what am I saying, this is German schools), the blackboard in every classroom was a large, green, rectangular middle part and two square "wings", one on each side (as wings are wont to be...). They can swing in and out, providing extra room for writing on the outer side of the wings. Also for extracurricular shenanigans such as writing "[name] + [name] = SEX" in the middle, swinging the wings closed to hide the writing and then breaking out into hysterics when the teacher opens the blackboard to reveal your incredibly highbrow joke.
This type of blackboard is quintessential to my recollections about and concept of school.
Why am I going into such unnecessary detail about this? I have ADHD and possibly autism, I need you to understand what I'm saying and I can't find any sources of this existing in the English speaking world and I can't find an English word for those "wings" either. I can barely find a German one ("Tafelflügel"? I don't think it's ever come up before in my life).
So here's a picture:
The width/height of the "wings" and the height of the middle part, that's a metre. Thank you for coming to my TED talk.