Yes I use a calculator. I'm using the 15mg very sparingly but probably will cut it down. Me and my girlfriend are still on the first tank from two days ago that we are sharing, we both just take a puff or two when we are craving a cigarette as we both still have an occasional cigarette and want to stop. So that's the reason behind the insanity.
My advice these days is to use WHATEVER nic strength you need to keep you off those disgusting toxic cancerous stinkies. Be it 36mg.. 50mg.. Freebase.. salts.. Whatever It takes. Remember, it's not the nicotine that is the problematic part - it's those stinkies.
Obviously, try lower first - then increase if need be. Once you reach a point where you're not reaching for the stink for a while, then you can start slowly lowing it.