Thank you! It’s not my very first but probably my first in ten years. I suddenly found I couldn’t ‘get’ some of the setters and really struggled, so after years of just doing ok I gave up. But... I’ve started again and today I actually finished the puzzle! And kind answers are always a great boost to the confidence!
I always took the HE to be an acronym for High Explosive - in what sense to you mean it?
I'm currently two thirds of the way through "Why does E=MC squared" by Brian Cox and Jeff Forshaw so am learning all sorts of stuff about energy and explosions.