On Vernier and Micrometer Calipers

November 26, 2010; 9:00-11:30; NIP R108

A Vernier and micrometer caliper were assigned to each group of 3 (which was determined last meeting; my groupmates are Mac and Peter). After the preliminary survey regarding the previous topics, Sir Aleo discussed about how to properly read caliper and micrometer readings. It is described by:

M.S. + F.S. * L.C. - Z = actual reading

where:

M.S.= main scale reading

F.S.= fractional scale reading

L.C.= least count

Z= zero reading

My experience on vernier calipers could be traced back to my 4th yr HS Physics Lab class. It was only then wherein we were introduced to vernier calipers and micrometer calipers, devices which offer greater precision than standard rulers and meter sticks. In our school, only calipers were available, and not micrometers. Thereby, before this physics meeting, I knew how to use vernier calipers, and not micrometer calipers.

It was the first time ever wherein I lied my eyes upon the micrometer caliper, a peculiar device that looked like a stick with an arch on one end. I also had a hard time comprehending how to use the device since it was the first time that I've seen it in my life.

After the lecture, we were given our activity sheet as a group. The activity entailed three sets of mini-activities. The activity's premise is basically the measurement of the length (L) and thickness (T) of rice using the vernier caliper and micrometer caliper, and then applying our knowledge on best estimates and Gaussian distribution.

The first mini-activity is the measurement of L & T of a single grain of rice, measured with both the vernier and micrometer calipers. Using the vernier caliper was easy, but the micrometer caliper proved to be excruciatingly difficult. The micrometer caliper's mechanism involves a screw which needs to be rotated over and over again so that the measured object would lock into place for measurement. Since a grain of rice is very irregular in shape and relatively soft, it was difficult to lock it into place. Therefore, we resorted to perform the 3 mini-activities with the vernier caliper first, then when we finish, with the micrometer caliper.

The second mini-activity is the measurement of L & T of 10 grains of rice, and then presenting the final measurement as a best estimate. We took turns measuring with the vernier caliper, and it seemed that we had good chemistry as a group.

The third mini-activity is the measurement of L & T of 10^2-10^3 grains of rice, and then presenting the final data as a Gaussian distribution. At first, it appealed to me as a joke because it was very tedious to measure 10 grains, what more if the number of grains is in the second or third order of magnitude. We took turns yet again, and eventually reached 70 grains with the vernier caliper.

We finished the lab meeting with tired arms and a hungry stomach. Even if the activity was a bit tedious, it allowed us physics students to gain insight on what experimenters feel. Measuring a great number of specimens is difficult, that's for sure.

We will continue the activity next meeting, and when we reach 100 grains for vernier caliper, we would start everything again for the micrometer caliper.