OneGuyFromBarlick

No takers at all.... Oh Dear!
I have always contended that the best way to understand the Roman incursion into the Isles is to regard the invaders as a heavily armed civil engineering organisation. The seem to me to have spent more time building than fighting. The mystery object is a Roman surveying tool. I'm sure Peter was on this because he hinted at levels.
Next for shaving?

You're not going to get away with it so lightly. How does it work?

Lining up the strings would give you a horizontal 90 degrees or a straight line. I believe these were used in conjunction with 3 long sticks for setting out straight roads.

If you think you can sit there saying nothing and then start issuing orders you've got another think coming!
I think Kev is on the right lines. It's called a 'Groma'. See THIS Link to an article on use.

What is it?

A machine vice for holding irregular shapes, possibly castings?

Exactly right Gloria but it has a specific name. That's what I am after. The banana is a clue.....

No idea.

Matrix, or is that a brand name for it?

That will be the brand. There is a name for this design of vise. I hadn't heard it before last night....

X-clamp?

No Gloria. The banana is a good clue because that's where I learned about it....

Don’t know, I give up.

Oh dear.... Big clue Gloria. 'Put Banana vise' in Google......

Never heard of this, a fractal vice.

That's right, easy wasn't it! Like you Gloria, I had never heard of it until I saw Eric refurbishing one on Hand Tool Rescue (LINK). A fascinating tool.
Next one?

What exactly is this?

Looks like something from a horror film for drilling into someone's head

Big Kev wrote: ↑27 Jun 2021, 12:57 Looks like something from a horror film for drilling into someone's head

That was my first thought,too, so is it a medical instrument used in brain surgery?

You are both warm, yes it could be used that way but not usually. It has a Proper Name!

It's an angle-of-dangle-ometer for measuring distance and angle from a sphere's centre. A tool for measuring in 3-dimensions - azimuthal, radial, and axial values.

Sounds good even if I don't know what I'm talking about!

Surgical Head Frame / Skull Clamp .
Neurosurgery .

You are all right but I'll have one last go.... There is a Proper Name for it, what is it?

Leksell Stereotactic System

Big Kev wrote: ↑28 Jun 2021, 13:49 Leksell Stereotactic System

Wow!