Final answer:
A vacuum gauge, such as a manometer, is the best instrument to determine the level of achieved vacuum.
Step-by-step explanation:
The best instrument to determine the level of achieved vacuum is a vacuum gauge. A vacuum gauge is a device used to measure the pressure in a vacuum. It can be designed to measure both positive and negative pressure.
For example, in physics experiments that take place in a vacuum chamber, a pressure gauge is used to measure the negative pressure inside the chamber. The pressure gauge on the chamber reads a negative value because it is less than atmospheric pressure.
An example of a vacuum gauge is a manometer, which is a U-shaped glass tube partially filled with mercury. One end of the U-tube is connected to the gas chamber, and the other end is either closed with a vacuum or open to the atmosphere. By measuring the difference in the levels of mercury, the pressure in the chamber can be determined.