MicrosoftIt also applies to MATCH and VLOOKUP. There, 'exact search' ran through each value in the lookup range until a match is found. For an range of 1000 cells this, on average, requires 500 comparisons. The binary (approximate) search applied to sorted data. The algorithm examines the value half way down the list and, depending upon its value, discards one half of the list or the other. This halving takes place until a closest match is found, typically requiring 10 comparisons for 1000 cells.
XLOOKUP has been written to take advantage of the efficiency inherent in binary searches even to the extent of sorting the data in memory where this leads to a performance gain. Somewhere early on in this thread I remember JoeMcDaid stating that he could not envisage circumstance in which the user would gain by explicitly selecting the search algorithm by using the final parameter setting of ±2.
