[avr-gcc-list] clock frequency, prescalers and timers

[Timothy Smith]

can anyone explain in simple terms how i can calculate the time it will 
take for the timer overflow interrupt to trigger using the prescaler? i 
have had success in  writing my own little programs to make various 
led's blink etc but doing this in terms of seconds or minutes still 
escapes my grasp of the concept.

lastly after all that, the board i have has a real time clock on it 
connected to T10, would it be easier to just use that to time things and 
if so an example of it?