MathCards is a simple game designed to help you memorize math facts. It works by asking you a question and awaiting your answer. Each individual question must be answered a certain number of times before it will be considered "mastered". At which point, you will not be asked that question again.
With your right hand on the number pad, type out the answer to the problem you see as quickly as you can. Be quick! You only have so much time.
While intended for use on a desktop or laptop computer, it will be styled to be functional on mobile devices. However, data entry may be hampered as the mobile device is not the intended target device.
You can click the "Download Mastery" button to save your progress as a .json file. When you come back, you can upload your progress and pick up where you left off.
Note that the number of correct answers to mastery and time to answer fields will not be saved as part of your progress. Start from the settings page and set those values, then load your .json file.
Technically, you can use any method to generate your .json file, so you could generate your own set of questions if you like.