setCPU lets you adjust the lower and upper speed for your CPU. There's a "device selection" function in the menu that lets setCPU perform all the computing and suggest the appropriate values for your hardware. Here's a screenshot for the Desire HD.
The "Time in State" section from the "info" tab lists the time your phone has spent at different speeds. From the following screenshot, it appears the Desire HD CPU speed scales between 4 speeds from 245 MHz to 1024 MHz, spending most of its time between the upper and lower speed. The same screen on the Nexus One shows many different speeds, the Nexus spending most of its time on the lower speed (it naturally depends on how you use your Nexus).
As said in its name, setCPU for Root Users require root access.Rooting instructions can be found here :
- Nexus One - CyanogenMod For Nexus One V184.108.40.206 (03/23/2010)
- Desire HD Ace : how to temporary root - [GUIDE] Temp Root [VISIONary by PaulOBrien]
Head to setCPU for Root Users's official page to get more informations on setCPU, specially on how to use setCPU to overclock / underclock your CPU.
Scan the following QR-code to download setCPU from the Android Market.