I’ve been travelling for work for over 20 years .. after a very very long trip in July (110 hours of travel in 14 days) I was exhausted for one entire week ... I decided to look for a better way to do this ... found this app .. waited for my next very long trip .. in a period of 17 days I had - Singapore, Japan, Australia,Singapore, Atlanta (USA) and back to Singapore (home).... I used this app to a tee on the singapore - Atlanta - Singapore portion .. ( supported by using sunglasses (when the advice was to go dark), and bright glasses when I needed bright light and there was no sun out (retimer glassses)... I had very little jet lag on the way over to the USA... and NONE on the way back to Singapore ... this is a first in travelling all my working life ..... brilliant, brilliant! If you travel beyond 3+ hours in time difference this app will really help ... highly recommended!!