The "Заточка ножей. Справочник." is a free Android app developed by Alexander Dubrovin. It falls under the category of Utilities & Tools and is compatible with Android 9.0. This app has a calculator that helps sustain the correct angle while sharpening knives. Additionally, it provides a handbook that assists in selecting the optimal type of sharpening for the blade's form and steel.

The handbook is user-friendly and provides a comprehensive guide to sharpening knives, including the types of sharpening, how to choose the right angle, and how to maintain the blade's sharpness. The calculator is easy to use and helps users to determine the angle and pressure to apply while sharpening. The app is free to download and does not require any in-app purchases.

Overall, if you are looking for an app that provides a comprehensive guide to sharpening knives and a calculator that assists in sustaining the correct angle, "Заточка ножей. Справочник." is an excellent choice.