In order to win a basic mandate, the party must receive enough votes to meet or exceed the Wahlzahl in at least one regional district. The Wahlzahl is not a number fixed by law, but is determined by dividing the total number of valid votes cast in the state by the total number of mandates available to be allocated for that state. The number of mandates apportioned to states varies because of large differences in population size. It is periodically readjusted based on the results of the most recent census to assure that each vote has the same weight regardless of there in the country it is cast.