Your first formula is complete, whereas the second one isn't. The IFS function needs to cover every possible situation, so in the second formula, it doesn't know what to do when the G6 value is less than 1.65. The documentation on IFS states that you can use an ELSE clause to handle any value not covered by the specified ranges. Check out this link: https://www.ablebits.com/office-addins-blog/excel-ifs-function/