Final answer:
To correctly use the HLOOKUP function with a TRUE lookup type in software like Microsoft Excel, the first row (key values) of the lookup table must be sorted in ascending order. This allows the function to perform an approximate match, which requires a sorted range.
Step-by-step explanation:
The first row (key values) of the lookup table must be sorted in ascending order to use an HLOOKUP function with a TRUE lookup type. The HLOOKUP function in spreadsheet software such as Microsoft Excel is used to search for a value in the first row of a table and return a value in the same column from a specified row. When using HLOOKUP with a TRUE lookup type, also known as an approximate match, the key values must be sorted in ascending order, otherwise, the function may not work correctly and can return incorrect results. For an exact match, where the fourth argument is set to FALSE, the order of the key values does not need to be sorted.