I have spent a long while trying to figure out how to calculate this and I think I figured it out! Please correct me if I'm wrong..

First, you take the NorthBridge Frequency and divide it by the DRAM Frequency:
In my case it is 3300/825 which equals 4

Then you take the NorthBridge Frequency and divide it by the BCLK:
3300/165 which equals 20

Lastly, you reduce:
4:20 = 2:10

But 4 can also go into 20.. so I'm a bit confused..

The ratio 2:10 is what is displayed in CPU-Z. Is this just a coincidence that I managed the same numbers? You can reduce further to 1:5.. why isn't this shown in CPU-Z?