Using Timer with event

Question

Hi,
To better understand the use of Timer and Events, I have built a mini application that is supposed to write the time every preset interval, using the Timer class.
It works for me, except that I get the writing doubled each time.
I have tried hard to understand the reason, but for no avail.
Can anyone run the attached small app and let me know what have I done wrong, or how to make it write the time one per line?
Thanks in advnce