I still occasionally listen to it.

https://store.steampowered.com/app/813230/ANIMAL_WELL/

This means the frame must be chosen and fitted to you before any of these are measured.

It becomes a 2D measurement.

There is a lot more to it (vertex distance, pantoscopic tilt etc) but the above is the absolute minimum.

I also agree with educating yourself to protect yourself. However, there will be many holes in your research which a good optometrist should be able to fill in. Together you can make the best choice.

One area I never see discussed, especially from the "I can find my own prescription" crowd, is binocular vision. How your eyes work together at certain distances and with certain tasks will determine not only which prescription you need but also how the spectacles are set. I'm not only talking about setting the PD and lens height (which may need to be different for your right lens compared to your left, at different at all distances). There are many more considerations such as vertex distance, pantoscopic tilt, frame choice, lens material, wrap angle etc.

Sometimes the optical centration is intentionally different from the PD to induce prism to decrease eye strain. This is not uncommon with complex prescriptions and in the older population.

And sometimes there are other solutions such as vision training. Not the woo woo Bates method, but real vision training used to fix real problems.

Good optometrists provide a lot of value. There just way too much information and most patients will be happy to just let them do what is needed.

And sometimes you just need to get off the PC for a bit.

However, where the optical centre of a lens is placed within a frame can vary from the PD a fair bit, depending on how the frames sit on your face, as the contact point of the frames do not always line up perfectly with the top of the nose bridge.

Also, an oft looked over measurement is the distance from the bottom of the frame to the centre of the lens, which is important with complex prescriptions and cannot be measured without looking at the frame on your face.

Having said this, with most low prescriptions the human tolerance is so high that it does not matter.

However, due to the selling point of Trivex being "shatter proof" it has a greater centre thickness (to pass safety lens regulations), and thus the edge thickness is also comparable to CR-39.