i am little bit confuse in automatic fixed pegging and dynamic fixed pegging

i am little bit confuse in automatic fixed pegging and dynamic fixed pegging

1) In automatic fixed pegging pegging is stable between receipt and requirement element . But I observed that some  production order of other sales order pegs to my sales order  when it is automatic fixed pegging . so how can it be stable

2)when I create manual planned orders it comes under dynamic pegging but these are also stable when it pegs to sales order

3)Give me exact difference between on these pegging

thanks in advance

Regards

Virender