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Scientific Measurement Instruments: Types & Uses

Instructor: Julie Zundel

Julie has taught high school Zoology, Biology, Physical Science and Chem Tech. She has a Bachelor of Science in Biology and a Master of Education.

There are many valuable measuring devices in science. This lesson will highlight how to use three such precision instruments: Vernier calipers, screw gauges, and physical balances.

Precision and Accuracy

It's Saturday night. Sure, there's a lot of fun stuff you could be doing, but probably nothing as fun as measuring using precision instruments. Intrigued? Well, precision refers to the repeatability of a measurement. If you were to measure something over and over, you would get the same or very similar measurement each time. These tools also make an accurate measurement, meaning that the measurements are close to the actual value. In other words, the measurement you get is close to the true measurement of the object. So, if I haven't convinced you to forego an evening with your friends, stay tuned. You'll be sold. Soon.

Vernier calipers

Our evening of fun begins with Vernier calipers, which are used to measure length and are made of jaws and a scale. Vernier calipers can be used for external measurements, like that of a washer, or internal measurements, like the diameter of a hole in a piece of metal or wood.

Vernier calipers measuring a washer
verne

Before we practice measuring with the calipers, check out just a few examples where calipers are used:

  • In vehicle mechanics to measure the thickness of various objects, such as brake rotors.
  • To make precise measurements in a science lab; for example, measuring the thickness of a fossil.
  • In the medical field, a special type of caliper is used to measure the percent body fat on an individual.

Okay, now let's kick off this measuring party by conducting some measurements.

Measuring using calipers
meacal

  1. Begin by zeroing out the caliper. Close the jaw so it is at zero. If you don't do this, your measurement will start at a different point and be off by a few millimeters.
  2. Now fit the object (in this case, a circle) snugly in the jaws by sliding the jaws open or closed.
  3. The measurement you see will tell you the first whole number and the first decimal number. The whole number is 3.
  4. Next, see where the zero on the lower sliding scale lines up on the top main scale. It looks like it is at the 5th line (count the little lines). So it is 3.5, but you're not done.
  5. Find where any line of the bottom sliding scale matches up exactly with any line on the top main scale. If you look, the lines match up at the 2 on the lower sliding scale (which means 0.02 on the scale). So, 3.5 + 0.02 = 3.52, and the answer is 3.52 cm.

Now wasn't that a blast? Let's check out another precision measuring tool, the screw gauge. And don't worry, using the screw gauge is pretty similar to the calipers.

Screw Gauge

The screw gauge is used for precision measuring, like the calipers, but typically it is used to measure objects smaller than those that are used for the calipers. The screw gauge tool is u-shaped and the object you want to measure fits between the anvil and the spindle.

Parts of a screw gauge
Parts of a screw gauge

Some areas where screw gauges are used include:

  • In telescopes to measure the size of celestial bodies.
  • In microscopes to measure the length of bacteria and other microscopic objects.
  • In the electrical field, they are often used to measure the thickness of wires.

Let's practice reading this nifty tool.

  1. Like the calipers, remember to zero out your tool. What if you close the spindle and it doesn't read zero? Well, that means you need to calibrate it. You can use a wrench to turn the sleeve until the reading is zero when the screw gauge is closed. Then you can measure an object with a known length to make sure the screw gauge is calibrated correctly. It's not a bad idea to check all of your precision tools before you measure.
  2. Start by placing the object you want to measure between the spindle and the anvil. You can open the spindle by turning the knob next to the thimble.
  3. Now read the top scale on the sleeve. On this particular screw gauge, the top scale goes by 0.5 mm and the bottom scale goes by 0.25 mm. So if you read the measurement on the sleeve, it is 0.5 on the top scale and one additional line on the bottom scale. This means 0.5 + 0.25, or 0.75 mm.
  4. Now read the thimble and see where the lines meet. This is at 10, or 0.10 mm.
  5. Add these all together: 0.75 + 0.10 = 0.85 mm.

Reading a screw gauge
Micrometer

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