A threshold table answers a different question from an exact identifier lookup. It may need to find the largest threshold that a measured value has reached. Make that selection rule explicit before using the returned position to choose any label or action.

In a separate Numbers practice table, put ascending numeric thresholds 0, 10 and 20 in A2:A4. Give them clear meanings in neighbouring notes, but keep the first trial focused on the position returned. Put the value to assess in C2.

MATCH(search-for, search-where, matching-method) returns a position within one row or column. Method 1 finds the largest value less than or equal to the search value and requires ascending search data. Method 0 seeks an exact match. State the method explicitly; omitting it defaults to method 1.

Try just below, on and above a threshold

Enter =MATCH(C2,A2:A4,1) in the output cell. With C2 set to 9.9, the expected result is 1 because the applicable threshold is 0. At 10, the expected position is 2. At 10.1, it remains 2. At 20, it becomes 3.

The result 2 means the second item in A2:A4; it is not the worksheet row number and it is not the threshold value 10. Keep that distinction clear if another formula will use the position to select an associated description.

Compare method 0 using a search value of 10.1. There is no exact threshold of 10.1 in the example, so an exact-match error has a different meaning from the valid approximate result 2. Do not change the method simply to suppress an error without agreeing on the intended rule.

Define the edges of the real decision

Decide what should happen below the smallest threshold and beyond the useful range of the table. A successful approximate match at a very large input does not prove that the report is intended to handle unlimited values. Validate the input domain separately.

Preserve the ascending order when maintaining the threshold list, and check any associated labels against their thresholds. Repeat the below/on/above trial whenever a boundary changes. Record whether equality belongs to the new level so another editor does not reverse a deliberate boundary policy while trying to make the formula seem more exact.

Reference: Apple: MATCH function.