Which of the following descriptions about measurement instrument is incorrect?
① When the micrometer is not used, it is necessary to separate the anvil and spindle measuring faces.
②When measuring something with a caliper, it is better to measure the object by using a portion near the
main scale.
The sensitivity of level refers to the change of gradient required to move the bubble by one carved notch
in the bubble tube.
③The sensitivity of level refers to the change of gradient required to move the bubble by one carved notch
in the bubble tube.
④ Lever type dial gauge is not suitable for measuring in a narrow space.