select sum() is not giving the correct sum

I have table with the following columns:
customer int4 NOT NULL
amount float8 NOT NULL

And among others I got these rows:
customer..amount
1118........9907.6
1118........29722.8
1118........-9907.6
1118........-29722.8

the correct sum for:
select sum(amount) from myTable where customer =1118;
should be 0. But the sum I get is 3.63797880709171e-12

I get this result from pgAdmin (running on Win2000), from my Delphi application and from psql running on Linux. I have also moved the same database to Win2000 using Cygwin.

Do anyone have a solution og explanation?

- Eirik

Explanation: float fields are stored in scientific notation and as such are subject to rounding errors, which is what you are experiencing.

Solution: use NUMERIC