where usually p ∈ [-2, +2] and c offsets any negative or zero value.
If min(y) > 0, the tool sets c = 0.
If min(y) ≤ 0, the tool sets c = 1 + |min(y)|.
Therefore, the tool returns three possible transformation scenarios:
if 0 < min(y) < 1, then min(y*) < 0
if min(y) ≥ 1 then min(y*) ≥ 0
if min(y) ≤ 0 then min(y*) = 0
where the first scenario returns negative values.
If you are working with data where 0 < min(y) < 1 and for some reason the transformed data must be non-negative, check the non-negative checkbox before submiting the form. This instructs the tool to set c = 2 + |min(y)| and min(y*) ≥ 0.