RealTemp reports an averaged multi at idle. If you are using Speedstep and have that properly enabled within your bios and within the Windows power management settings, a Core i7 will show a steady multi of 12.0 at idle. If you don't have those items set properly in your bios and within Windows, RealTemp will show an average value that floats somewhere between 12.0 and your full Turbo multi. If you want it to be steady at the full number then you have to set your bios and Windows accordingly. Turn off C1E and Speedstep in the bios and make sure your Minimum processor is set to 100% in the Power Management section of the Control Panel.

When RealTemp reports 16.0 that is a sign that the multi is constantly changing between 12.0 and your full multi.
16.0 represents the average.