We've been using Vernier callipers to make measurements. There are two scales. The fixed scale has a resolution of 1mm but is actually marked in cm on these callipers. The sliding scale has not numbers on it and is etched into the bottom of the window.
The left hand mark on the sliding scale is used as the marker for where we are on the fixed scale. I've used a red arrow to show this. The asterix marks the 1mm mark. Our marker has just gone past it so we have a reading of of 1mm + a bit. We get the bit by seeing where the marks on the two scales actually line up. I've marked that in green. I now count how far along the sliding scale that happens: 5 marks. So my reading is 1.5mm. This Vernier scale allows us a resolution of +-0.1mm.
