BEWARE!! Some idiot on that site: The Vape Book has their recipes' Nic Juices' Nicotine concentrate listed as 20%!!! I don't think that's really what they mean... I think they meant 2%, or 20mg/mL for Nicotine concentration. REMEMBER 12mg Nicotine/mL of juice Equals 1.2% Nicotine in 100% of the juice overall. I just don't want to post a link to a site where they've let a typo like that get printed.
20%? Um... URK!
Though the one I found, they look like they mean 20% of the total volume. Such as 3ml of nic juice in a 15ml mix. Definitely doesn't look like a "beginner" site...