No biggie- it wouln't be such a big deal for you to get yourself a real vernier after all.

Wing some engraving facility on your mill: just bolt a small aluminum plate (subscale-to-be) to the table,
put some engraving point/ scriber in the chuck and go.
You could make the subscale to reach up to the 39th scale point (say in 10 divs with 1/2 sub-divs in between),
so that it'll be real easy to read, minimize parallax, and it'll give good resolution down to 1/20 graduation.

Two cents
Johan