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I need an application that will help with my interval training. I'll try to explain in a practical way(hopefully)
I run really fast for 20 seconds and as soon as the 20 seconds are over i change to a normal running pace for 40 seconds, after that i just rinse and repeat, without stoping ofcourse.
So, what i would like the application to do is sound an alarm when i change intervals, which means 20 seconds after i start, 40 seconds after the first 20 second interval is over, 20 seconds after the 40 second interval is over and so on and so on.

So, any ideas?