1.) Tap the little "T>" at the Top Right corner of CALC and you will see a running clock
2.) There are two buttons at the bottom to switch the Timer ON or OFF and to control the Clock sound
3.) When you Tap "TIMER OFF" a popup shows up to set the number of minutes.
After the Timer is enabled, you can see it running live on the screen.
If you tap the timer screen, you will get back to the calculator and the timer will be running Live in the top right corner.
Finally, if you suspend the app or your phone, a Notification will pop-up once the timer has finished!