This is a classic case of a spreadsheet doing exactly what you told it to, and exactly what you don't want it to. The `#CALC!` error appearing in column O isn't a sign that your formula is broken; it's a sign that your formula is working too well. You built a precise lookup using `IFS` and `TOCOL`, and when the input cells are empty, the function has no data to evaluate. It errors out because it has nothing to calculate. The fix is not to rewrite the logic, but to add a simple guard: check if the input exists before you ask the formula to do its job.
That guard is an `IF` function wrapped around your existing work. The principle is straightforward: if either cell K7 or L7 is blank, return nothing. Otherwise, run the `MIN(TOCOL(IFS(...)))` calculation. The practical implementation looks like `=IF(OR(K7="",L7=""),"",MIN(TOCOL(IFS(K7:L7={15;22;28;35;42;54;67;76;89;108},{11.39,11.39;11.68,11.68;11.96,11.96;13.08,15.2;14.02,16.35;15.77,18.22;17.17,19.57;20.62,25.63;24.34,28.59;31.25,36.09}),2)))`. This is the standard pattern for silencing errors caused by missing inputs. It's not a workaround; it's a design principle. Your spreadsheet should be silent when data is absent, not noisy.
What this reveals is a larger truth about building durable spreadsheets. The complexity of your formula, nested arrays, two-dimensional constants, and a `TOCOL` conversion, is impressive, but it also creates fragility. Every layer of logic is a potential failure point when data conditions change. The real skill isn't writing a formula that works perfectly with perfect data; it's writing one that behaves gracefully with imperfect data. Blank cells, unexpected text entries, or even a single space character can cascade into errors that take hours to trace.
Your instinct to ask for help is exactly right. The solution here is a single `IF` wrapper, but the lesson applies everywhere. Before you build a complex lookup or a nested calculation, ask yourself: what happens when the input is empty? What happens when it's the wrong type? What happens when it's a zero? Answer those questions first, and your formulas will stop surprising you. The `#CALC!` error is not a bug; it is feedback. Listen to it, and then wrap it in a condition that makes your spreadsheet work for you, not the other way around.