calc.pw is somewhat easy to use. Instead of connecting the keyboard directly to the computer you connect it to calc.pw and then you connect calc.pw to your computer. During startup calc.pw displays some information about itself.
When startup is complete calc.pw asks for the master password. This one is necessary to calculate the service passwords later on. The password you enter here will not be shown but it will be masked with asterisks instead. The arrow on the right side tells you whether a new character was added to the password or if it was removed by pressing the backspace key. During this mode only the red LED is switched on.
After you entered the master password by pressing the return key calc.pw asks for it again. By entering the master password for a second time you can make sure that you really entered it correctly. Only if both password entries match you will proceed to the next mode. If you enter a wrong password here you will start with the first password entry again. In this mode the yellow and red LEDs are switched on.
When both passwords match calc.pw switches into the usage mode. In the so-called passthrough mode calc.pw forwards all key presses directly to the computer without modifying them in any way. In this mode the green LED is turned on. By pressing the key combination CTRL+ESC you switch to the password generation mode. Here you are requested to enter the service-dependent information. You can use some password features when entering the information. The password features are described in chapter 3. How do I have to enter the information?. In this mode the green, yellow and red LEDs are turned on.
To finish the entry of the information there are two possibilities. The first one is to press CTRL+ESC again and the second one is to hit the return key. The difference is that pressing CTRL+ESC will just generate the password while hitting the return key will also send the return key to the computer. This comes in handy when filling out a login form as you do not have to press the return key again to finish the login process. During the calculation of the password the green and yellow LEDs are turned on. When the password calculation is done calc.pw automatically switches to the passthrough mode again.
In addition to that calc.pw has a reset button. calc.pw will reboot when this button is pressed for a longer time. During this reboot the master password in the Arduino's memory will be overwritten. This is helpful when you have to leave calc.pw unattended and do not want others to be able to generate passwords with your master password.