For the Youth...
Sharing a project that I've made for when we go to schools and outreach events. As a small group of advocates who don't get paid for it- sometimes getting equipment is a pain.
Here, we can show how compression waves read wall loss. Laser is just a visual aid and not reading the distance. I have other samples that from the front they all look the same- but as you scan them you can see corrosion/Erosion, and lamination.
Some cheap electronics and about 1kg of filament.
Add some increments at the top and they could sketch the corrosion...