Pharmacy Tech Students taking BP?

It's always fun to teach a task that was learned 39 years ago. I am talking about taking blood pressure. When I learned to do this, we actually used a device that had mercury (Hg) in it. We learned that 120 over 80 millimeters of mercury was desireable. Now when we teach it, we must explain why it is/was called mm of Hg. Students seem to love the fact that I am so old I've "lived" the changes in drugs and devices.