In reply to Graeme G:
No idea about TPE however I do like and use Photopills.
I especially use the shutter calculator for astro photography which uses the NPF rule which is way over my head and makes my tiny little brain explode trying to understand it. Its far more precise than the 500 rule, 450 rule or even to 300 rule which were all designed for analogue film cameras rather than precise camera sensors with pixels that are less forgiving with movement of stars.
I also use the Augmented Reality of showing me where the sun is going to set or pop up by overlaying its path on a live display of the landscape I'm physically looking at.