The rules are simple:
In the SETUP view you can pick one or more digits (preset to digit 3). In the main PLAY view a counter will constantly increase its value by one. You and your smartphone/tablet/... take turns. If the current number on display contains one of the selected digits you have to call (here press) BUZZ . Also, if the number is a multiple of any of the selected digits you have to
press BUZZ as well. If not, press NUMBER instead.
For example, you have selected digit 3 in the SETUP view. Then it is a BUZZ, if the current number is 43 (it contains the digit 3) and the same is true for 27, for example, as 27 is a multiple of 3 (3 * 9 = 27). Of course, if you select several digits, things can become difficult.
That's it. Sounds straight forward, but don't be fooled - the game can become quite challenging!
There are a few more options in the SETUP view. You can adjust the speed of the number increment. This sets the time interval, wherein you have to decide whether to press NUMBER or BUZZ - if the time expires, you lose. You can turn on or off the number display or the voice output.
Finally, you can turn on the training mode, the device will track the number of errors you make, but it won't stop the game.
For every combination of digits and speeds the app will keep track of the high score you have achieved (you can erase the high scores in the SETUP view, if you like).
There is a kind of cheat option - you can press PAUSE anytime during the game to give yourself more time to think of the right answer, the app won't punish you for that.
The app opponent plays a perfect game, so the goal is to reach the highest number before you make your fatal mistake.