code: def x(self, x):
          
          if x is None or x <= 0 or self.log10_xmax - self.log10_xmin == 0:
              return None
          return (
              self.width * (log10(x) - self.log10_xmin) /
              (self.log10_xmax - self.log10_xmin)
          )
docs: Project x