In order to gain a seat in Parliament, a political party needs to obtain a minimum number of votes, the so-called electoral quota. This is the overall number of votes cast for all the candidate lists divided by the number of seats in the House of Representatives (150).
Seats are allocated as many times as the total vote for a specific list (political party) contains the electoral quota, but this never comes out exactly. Any remaining seats, known as residual seats, are allocated according to a system of highest averages. To be awarded a residual seat a party must have gained at least one seat on the basis of the electoral quota.