The first two arrows help you get the measurement in mm. The third helps you read the decimal. The Vernier caliper is a standard method used in instruments to get higher precision readings. As discussed in section 1.4, the method used in making a measurement determines the accuracy with which the numbers are reported. This simulation allows for a reading to the tenth of a mm.
Calipers commonly used in industry provide an accuracy to the hundredth of a mm.
Fu-Kwun Hwang Go to the web site and link to the Online Library for further information.