The Creature Codex (and the Wizards article it's from) say
But everyone always draws them with two eyes and a mouth on the front and not much on the other faces.
Thanks, Rip!
So how are they organised, I wonder? I would guess that they devote each face to a different type of sense. I'm thinking Auditory environment (hearing), physical environment (measuring equipment, levels and such, maybe temperature), physical characteristics (hardness, texture ect.), chemical environment (smell, psychrometer), visual environment (eyes and lenses with different opacities, ect.), relative environment (position, compasses astrolabs, planar sextant), and chemical characteristics (taste and others). That's seven things.
I'd put physical environment on the botom (levels built into the feet, ect), Auditory on top (mental image of a Quadrone listening in on a conversation with four different styles of ear and a hearing trumpet cocked), chemical environment on one flank, physical characteristicts on the other, and positional on the back. Its eyes already are on the front, and its mouth and "digestive" tract probably handle chemical analysis of samples.
Am I stupid or do Quadrones have wings? I thought it was only Nordom and a few others who had the four arm specification (yes, im identifying Modrons as if they were computers which I know is a bad habit 
)
And arent they cubes?
Just general thoughts...on how wizards are messing with things :s
Hugz
B
)A plurality of quadrones have four arms, but some have two arms and a pair of wings.
Rogue modrons always have two arms and a pair of wings, unless they get themselves refitted.
Yup. Six-sided Euclidean shapes.
So then (being the pinnacle of law) they cant be rectangles? Thats my point. If one is a cube wont they all be cubes? If wizards are messing about and making them cuboid (as is my understanding of geometric conversion of rectangle to 3D) then thats just silly.
B
A rectangle is defined as a quadrilateral where all four of its angles are right angles.
A square is a kind of rectangle.
All six faces of a quadrone are squares.
You may be thinking of Duodrones. They are refered to as being rectangular and have wings.
Huh. And, aparently, the general name for rectangular cube-thing is rectangular solid. Cubes are rectangular solids with square faces. Rectangular solids aparently have all right angles. I love google.
Their other sense organs don't look like eyes or mouths. They're more likely to look like antennae, compasses, astrolabes, psychrometers, thermometers, measuring tape, levels, slide rules, and other mechanical devices.