Pentium M/Centrino proc running at less than full speed

[Bioture]

Hey guys, I recently got a thinkpad, and when I rightclick on my computer and go to properties, it says Intel(R) Pentium(R) M processor 1.70GHz, but on the bottom it fluctuates between 1.69GHz and 1.39GHz. Why is this? Is there something wrong with the proc or does this just show the true speed of the proc and it lowers its speed to save battery?

[Mulkero]

The point of speedstep is to save battery and avoid heat. If the processor is not needed, it will run slower and your laptop will stay cooler and quiet. When you need some power, it will run at full speed. My Pentium M is at 1.73GHz at max