In essence its a repeat of the ppl, as you need to be satisfied that the new type can be correctly handled exactly the same as any earlier type ratings. Emergencies, limitations and any new bits (eg hydraulics) are also covered as is some theory concerning the new aircraft(walk round and aircraft systems). Some sections require more time than others depending upon the students previous experience. Extra bits required on turbine theory if its somebody's first turbine rating, and a first twin rating will involve a lot of systems theory and performance discussions.