Grid Slice

I've puzzled it out now and think I've decided why McD's fries are of different lengths but perfectly proportioned in width and depth. Imagine a grid made out of metal as sharp as a razor. Now imagine that grid knife stamping down on a potato shape standing up on its end.

So here's my theory: McD's mixes a concoction of lab chemicals and salt into a paste-like substance that is poured into potato molds which are later exposed to UVA rays or some other process that causes them to harden in the shape of a potato. Then they are sliced on a conveyor by a robot arm with a grid knife, just before traveling through the tunnel of golden brown paint sprayers. The result would be fries of near perfect width and depth proportions (though a few would be triangular) but varrying in length.