output of negative zero values

Hi,
On using rekall to generate balances and totals etc, but one thing i've 
noticed on large calculations is the negative zero values i.e -0.00
The calculations are only additions or subtractions, the balance should really 
be 0.00, What would cause it to produce -0.00? I noticed this with scalc too, 
but if i do the calculations within postgres it produces 0.00, the datatype 
is numeric(10,2). Any ideas getting it back to 0.00?
Jewels