question about online beam calculator vs equation

Hi! I was working out how to determine the stress and deflection of a length of aluminum hollow square section tubing. Doing pretty good until I tried to match the results of one of these online calculators and my own calculations using the equation given. I get a result of half the stress. Usually I think the tool is broken until I learn what my own mistake was, so I'm hoping you'll help me spot it.

Here's the deets:

online calculator here: [url]https://www.engineersedge.com/beam_bending/calculators_protected/beam_deflection_2.htm[/url]
stress equation here: [url]https://www.engineersedge.com/beam_bending/beam_bending1.htm[/url]

I wanted to verify my own calc on 'stress at any point,' the figure given by the calculator was -6388.889, my result was -3194 (half!)

attached is an image with my variables included: I=.9, E (irrelevant for this portion) = 10,000,000, distance to centroid=1

thanks for having a look!

[IMG]https://www.engineersedge.com/engineering-forum/attachment.php?attachmentid=2052&stc=1[/IMG]

The equations that go with the calculator are here:

[url]https://www.engineersedge.com/beam_bending/beam_bending2e.htm[/url]