How to center the positioning vise under your scope. No gadgets
needed. - Clamp the part to be engraved in the vise. Move the scope over
the vise and spin the vise quickly. While looking in the scope, move
either your microscope and/or the entire vise around what you have it
sitting on until the spinning blur you see in the scope is in the center
of your field of view. Looking into the scope and spinning fast provides
cross hairs to aim for. The center of the blurry spinning image is the
cross hairs.
I have been using scopes with boom stands. A boom stand consists of a
horizontal arm and vertical post. The nice thing about a boom stand with
a positioning vise is that once you have the scope and vise centered you
can swing the scope out of the way, and then when needed swing it back
to the same spot quickly. Peak in and spin the vise to see when you're
back in place on the swing.
Here is a photo of a boom stand.