There are several methods to measure a person's sense of smell, including:

Sniff test: This involves presenting a person with a series of odorants and asking them to identify each one. The results of the test can then be compared to the expected results to determine the person's level of olfactory acuity.

Scratch and sniff test: Similar to the sniff test, this involves presenting a person with a series of scented cards and asking them to identify each scent. The results of the test can be used to assess the person's sense of smell.

Threshold test: This test involves presenting a person with a series of increasingly concentrated odorants and asking them to indicate when they can first detect the scent. This test is used to determine a person's olfactory threshold, or the lowest concentration of an odorant that can be detected.

Odor detection and discrimination test: This test involves presenting a person with a series of odorants and asking them to identify and differentiate between them. The results of this test can be used to assess a person's ability to detect and discriminate between different odors.

A person's sense of smell can be impacted by various factors, including age, illness, and exposure to certain substances, and can also fluctuate over time. As such, these tests should be repeated periodically to determine changes in a person's sense of smell over time.