Hi

I have a math. formular which needs some tweaking:

Code:
$row->res_no3 = (($row->input_no3 - $row->e_no3)/$row->perc_no3*100)*($tvolume/1000)/$row->dose_week;
Now it works fine.. but.. if e_no3 is higher than input_no3 it doesn't just result in '0' or null, it "starts from '0' again... meaning:

if
input_no3 = 10
&
e_no3 = 11

it goes below zero, and just displays the value for:

input_no3 = 1
e_no3 = 0

does that make sense? or am I babbling?

it goes into the negative numbers, and show that result.. just without the negative notation '-'

What can be done to prevent this?