Showing chronometer on PC controlling the begining and end of time by Arduino I'm really new on this Arduino thing, so I don't know whether what I'm gona ask is feasible or not.

I'd like to make a chronometer in the computer but the controlling button (beginning and end of count) not to be some computer key. So I was wandering if I could make a button controlled by the arduino - maybe via a piezoelectric element?

Besides the problem of not knowing what to use as a button, I don't really know if it's possible to make a graphical interface (i know how to programme in C, Python, ...) showing the numbers in the screen of the computer and the beginning and end of counting controlled by that button. Is this possible to do?

Thanks for any help to both questions!
It's perfectly possible to do, and the way I would probably do it is to use one of the ATMega32U4 based Arduinos (such as the Arduino Leonardo or the somewhat smaller Arduino Micro) to act like a keyboard. A keyboard with just one key - your chosen button.

Then you program the computer to respond to the keycode the Arduino sends to start and stop the chronometer. You could even use an off the shelf chronometer program that starts and stops with a specific keypress and tell the Arduino to send that keypress. It would probably take about 5 minutes to write the software - if that.