What is the reading shown? The diagram shows part of a micrometer screw gauge.

Option C - 5.81 is the correct answer of the reading of micrometer screw gauge in the diagram.
To get the first part of the measurement, look at the image above, you will see a number 5, this means 5.0mm.

Notice the extra line, this represents an extra 0.5mm.
5 + 0.5 = 5.5mm

To get the second part of the measurement, the number 30 on the rotating vernier scale is 0.3mm, notice an extra line after 30, this represents 0.01mm.

0.30 + 0.01 = 0.31mm

Add first and second part of the measurement to get the micrometer reading
5.5 + 0.31 = 5.81mm

The correct answer to this question is 5.81 mm. This type of problem would test how well one can read measurements. It uses a micrometer screw gauge to, and a micrometer screw gauge is used to measure instruments used for mechanical and metrological purposes. These instruments include dials and calipers.

The longer lined, and the vertical part of the indicator is how we get 5, while the horizontal and shorter lined section is how we get .81. mm in the answer stands for millimeters, which is one-thousandth of a meter. mm is the standard form of measurement in those industries.