I bought a USB microscope from China on Ebay. It shows a rather odd behaviour:
The microscope is being rotated about its axis. The text is not moving.
Note how the axis of rotation is around the 'f' rather than the centre of the image, as one would expect.
I sent the first one back because of this, thinking that the sensor had been mounted skew. This is the replacement.
It almost looks as if they're only reading part of the sensor. I'm wondering whether they're using sensors that have been rejected because of defects, and are just using the part of the sensor that is defect free.