Hi and welcome. I hope you got to do a walking tour of the rainforest in St. Lucia; very lush.
Dive computers readily handle multi-level dives (which is what most reef and some other dives are) to maximize dive time, give you a real time notice of how much NDL you've got left at your current depth, and if you get one that's air-integrated, it can probably log your start and end tank pressures, and some can log the dive and download it to your computer (or even smart phone with some dive computers). Diving existed before computers, but especially for multi dive days I can hardly imagine skipping one to use old dive tables.