In the formula you have you would need to record more than one value for each characteristic, i.e. 30, 32 and 34. If you have them as summarized results, I suspect that is where you get the error. Make sure all three characteristics are "individual results" and at least two results are recorded for each.
If you hope to get the maximum value of 30, 32, or 34 this will not work.
Craig
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