The default for the bias level is |dmin| + 1% * dmax. The value must clearly be at least as big as |dmin|, but if exactly that value is supplied then there are an infinite number of logarithmic decades between (dmin+bias) and dmax. ASMOOTH adds on another 1% of the data range, which will reduces the dynamic range in the data to two decades. By adding on smaller percentages of the data range in response to the BIAS prompt (ie. values less than the default but larger than |dmin|) a larger dynamic range will be retained.