Resistor Ratio Calculator is a free Android app developed by Peter Ho and falls under the category of System Tuning & Utilities. This app is designed to assist hobbyists and electronic engineers in calculating all possible resistor values to approximate a desired ratio for basic circuits such as operation amplifiers and voltage dividers. The app provides four main features. First, it calculates resistor values for voltage dividers. Second, it calculates resistor values for inverting amplifier gain. Third, it saves component values in CSV files (Excel files). Fourth, it allows users to use preferred values of resistors. The PRO version of the app offers additional features such as no ads, the ability to use preferred value 1% and 5% for resistors, and no limitations. It is important to note that users who need support should email the designated email instead of using the feedback area. Overall, Resistor Ratio Calculator is a handy tool for electronic engineers and hobbyists alike, providing a quick and easy way to calculate resistor values for basic circuits.