Making own timer like the system clock using battery

I think you really need to clarify your question. What is it you want to do? Do you want to develope a completely different piece of hardware and interface it to the parallel or serial port? In that case, this probably goes beyond the discussion of C#. What other system clock are you referring too? You would need to have some sort of embedded system that triggers an interrupt on your computer and acts like a clock. As far as I know, there is only one system clock accessible through windows, unless you create a new custom piece of hardware. My guess is in the .NET world, you would register this new piece of hardware (custom system clock) with WMI somehow. -Mike