I am an inexperienced diver looking for my first BP/W set up. I am looking at the DiveRite Transplate with steel backplate. For wing, I am looking at the Oxycheq Mach V. I am going to dive single tank but unable to decide whether I should go for 40lbs or 30lbs of lift. I am 120lbs. I know there is a calculator but I have no clue how to use it so can anyone help me ?