by Allen Wyatt
(last updated June 18, 2016)
Marissa works for a lab where she uses Excel to prepare client reports showing the results of mold spore sampling. The first sample shown is always the baseline. All subsequent samples on the report need to be highlighted if they are 10x the baseline. Marissa has this figured out if the baseline is greater than 0, but if the baseline is 0, the samples should only be highlighted if they are 10 or more. (In other words, a baseline of 0 and 1 are treated exactly the same for comparison and highlighting purposes.)
Let's assume, for a moment, that the baseline value is in cell A2. Chances are good that Marissa has developed a formula for her conditional formatting rule which compares the sample values (let's say they start in cell A3) with the baseline value, multiplied by 10, like this:
=A3 >= ($A$2 * 10)
This returns True if the value in A3 is greater than or equal to the baseline value in cell A2. The only thing that needs to be done to this formula is to make sure that the baseline value being used is never less than 1. There are any number of adjustments that can be done to the formula. For instance, the following uses an IF statement to evaluate the baseline value. If it is equal to 0, then it returns a modified value of 10.
=A3 >= (IF($A$2 = 0, 10, $A$2 * 10))
You could also use the MAX function, if desired, which returns the largest value from a series of values:
=A3 >= (MAX($A$2,1) * 10)
Note that MAX will return either the baseline value in A2 or the value 1, whichever is greater. In other words, the baseline value will never be less than 1.
Finally, you could avoid worksheet functions in your formula altogether if you simply rely on how Excel handles Boolean logic. Consider this formula:
=A3 >= ($A$2 - ($A$2 = 0)) * 10
This works on the very simple principle that, if the baseline value (cell A2) contains 0, then ($A$2=0) returns the value -1 (the value Excel uses for True); if the baseline value is anything other than 0, then the test ($A$2=0) will return 0 (the value Excel uses for False). This value (-1 or 0) will then be subtracted from the baseline and multiplied by 10. In other words, if A2 contains zero, the formula will be tested against 0--1, which equals 1, and so the test will be performed as if A1 contained 1.
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