Echo and X-Ray - International Maritime Signal Flag Concordance

The letter X and letter E, are called X-Ray and Echo.  In the modern day, Echo location and X-ray vision are important tools in science and military technologies.  When you take an X-ray picture, you are basically looking at an Echo of high frequency radiation.

The queer thing is that the names for the flags for Echo and X-Ray create a concordance, as a names of the flags pair up like salt n' pepper, Romeo n' Juliet.





Image X-ray
https://www.nibib.nih.gov/science-education/science-topics/x-rays

Image echo
https://www.yousigma.com/interestingfacts/whatisecho.html