Pool Difficulty Question

[sdhayes12345]

Currently mining on the notroll pool.  What does it mean when it says one of my worker's difficulties switches from 64 to 128?  Also, what does the first number in the accepted share cgminer report mean? Accepted [number] Diff x/128.  I can see that the 128 is the pool difficulty. 

If there is a link to a guide or resource that explains this better I would definitely appreciate it!