The smooth ruler is printed with clear scales, which could measure the inner and outer diameter precisely.
This vernier caliper is designed with small size and light weight that is convenient to store and carry, and it is easy to operate.
The tail of the vernier caliper could be stored in the groove of the ruler, you should use it frequently to avoid deviation caused by bent.
This kind of vernier caliper is designed with a wide range of application that could measure the length, width, inner and outer diameter of things, making your working easier.