Millwrights are often required to perform precision measurements. We need to evaluate machine components like bearing fits, or perform checks on incoming parts. Because some of us don’t measure all the time, or become used to measuring in one system (metric or inch), we sometimes get out of practice with reading some measuring instruments. Two of the most common precision measuring instruments are vernier calipers and micrometers (or micrometer calipers).
Vernier calipers have been replaced in many instances by digital calipers, but they are still used in many applications, so we are often required to read them correctly. Historically there have been a number of different vernier scales used, but the most common inch caliper is the 25 space Vernier. For practice reading this inch vernier caliper, try Prof. Eduardo J. Stefanelli‘s site below. Scroll down to the animated caliper and maximize it. If you click on the moveable jaw, you can control the measurement. Clicking on the eye in the lower right will show/hide the reading.
Metric Vernier calipers come in a number of styles too, but I prefer the 50 space type, that has a discrimination of .02 mm.
See Prof. Eduardo J. Stefanelli‘s site below for a practice example.
Inch micrometer calipers read to 3 decimal places, or incorporate a vernier scale that allows reading to 4 decimal places. Practice reading to both 3 and 4 decimal places on Prof. Eduardo J. Stefanelli‘s site below.
Metric micrometer calipers read to 2 decimal places, or incorporate a vernier scale that allows reading to 3 decimal places. Practice reading to both 2 and 3 decimal places on Prof. Eduardo J. Stefanelli‘s site below.
2 decimalplaces
3 decimal places