president that someone else has been elected to (As in case of death) can only be re-elected for one full term if he served more than 2 years in filling in for the original elected President.
That meand is someone died 2 years into his term, the VP can take over as President for the final 2 years then be re-elected for 2 terms of 4 years. Hence the 10 year maximum.
did better than me.... 
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