Hello, Swittie! Welcome to the Elsmar Cove!
Along the lines with the others, it's a little hard to imagine what all you would need. Just with one item alone that Jim listed, there are all kinds of optical comparators with many different functions. You may want one with a camera on it, computer interface, geometric dimensioning, etc. Or, you may just want a standalone, basic unit. It all depends.
What may be a way to go is to approach it from the other end: determine how much money (and space) you have, and then that will give you an idea of what you can purchase. I would give consideration first to the space and any environmental considerations.
Too, reviewing the different processes you currently have in place may also help in determining what equipment you will need.