Free Windows Desktop Stopwatch - very small and fast standalone application for measuring time intervals. It does not require any registration for download, decompression or installation. Just download it and run it. It takes around 0% of the processor time (you can check it with Ctrl+Alt+Del in your Task Manager) and almost nothing from your system memory. You can hide it in the system tray to free the screen space as well and show it when you need it.