I bought the apps from Precision for Bandits, Reef Runners, HJ , and Snap weights for $1.99 each and there Great. You can put in the depth that you want to get down to, or you can put in how many Feet Back and it will give you the depth. Get it for only the baits you want or get the lifetime app for $109.99.
I also have a old book and the app is much better.