As opposed to quota methods, divisor methods work with divisors other than the standard divisor . These divisors are called modified divisors. The modified divisors then divide the state's population to produce the modified quota.
Jefferson's Method
The method consists of finding a modified divisor, D,
so that when each state's modified quota is rounded down and all are added,
the the total number is exactly the number of seats to be allocated. Several
values of D might have to be tried.
This method is also known as the method of greatest divisors. Be careful... the modified divisors are less than the standard divisor, but they produce greater modified quotas, which are rounded down.
Adam's Method
Adam's method is very similar to Jefferson's method, but it uses a
modified divisor larger than the standard divisor,
which produces smaller modified quotas that are rounded
up.
Huntington-Hill Method
The Huntington-Hill method is also called the method of equal proportions,
and it is the method currently used to apportion seats in the U.S. House of
Representatives. If q is the modified quota, and q
is between integers n and n+1,
then the geometric mean of n and
n+1, which is the square-root of n*(n+1),
is used to decide whether to round q up or down.
If q <= sqrt( n*(n+1)
), then q is rounded down.
If q > sqrt( n*(n+1)
), then q is rounded up.