Answer what you know. Skip what you don't. This gives you a place to start, not a diagnosis.

Work down the list. Mark each one Found, Ruled out or Can't tell, and write what you saw. "Found" means worth investigating, not proven.

Use the same length of time before and after the drop. Percentages can mislead when the numbers are small.

Nothing you type leaves your browser. Your answers are kept on this device so you can come back, and Clear everything removes them. This tool does not know your site. It cannot tell you that an update caused a fall, or that a fall cost you enquiries. If most rows end up as Can't tell, that is a finding, and it usually means missing history or missing tracking.