What's the scale on Mars rover "Microscopic Imager" images ?

[B0b-A]

What's the scale on Mars rover Opportunity's "Microscopic Imager" images ?

I'm trying to work out if the Martian "fossil" shown could be the impression of a cross-head-screw ...

http://mars.jpl.nasa.gov/mer/gallery/all/1/m/3720/1M458433044EFFCEQKP2955M2M1.HTML

 

[Simon Bridge]

The MI is mounted on an arm and does not have a single resolution.
Certainly the images are pretty meaningless without it.

The consensus seems to be that the image is an impression of a screw from the base of the APXS - you can also see how the base has flattened the dirt and a section of it's arc.

 

[B0b-A]

It looks like a match ...

mars.jpl.nasa.gov/msl/images/apxs_portrait-br.jpg