I was given a tool cabinet and assorted stuff for helping an elderly gentleman move and downsize. In the mixed stuff is a depth mic that either his dad or himself had. It had been set aside and the rod was lightly seized. I applied light penetrating oil and finally got it to move. There was lots of light rust inside the spindle and in the hole that the rod passes through as well as the rod. I ended taking it apart completely. In resetting the rod my question how to calibrate? As per the photo it comes with 6 rods in total and I hope that the 5 long ones are correct. The shortest one was in the mic and I removed the pinch nut to clean and lube before attempting the reinstall. I will take it in to work and use some gauge blocks, but here at home I am getting some differences in readings. Mind I am using a dial vernier caliper. When I set the mic to 1" and the vernier agrees, I run the mic back to zero I see that the rod is actually slightly inside the anvil by about 0.003". Am I missing something?