docs: def bot_yformatter(self, val, type=''):
          """custom formatter for FuncFormatter() and bottom panel"""
          fmt = '%1.5g'
  
          ax = self.panel_bot.axes.yaxis
  
          ticks = ax.get_major_locator()()
          dtick = ticks[1] - ticks[0]
  
          if   dtick > 29999:
              fmt = '%1.5g'
          elif dtick > 1.99:
              fmt = '%1.0f'
          elif dtick > 0.099:
              fmt = '%1.1f'
          elif dtick > 0.0099:
              fmt = '%1.2f'
          elif dtick > 0.00099:
              fmt = '%1.3f'
          elif dtick > 0.000099:
              fmt = '%1.4f'
          elif dtick > 0.0000099:
              fmt = '%1.5f'
  
          s =  fmt % val
          s.strip()
          s = s.replace('+', '')
          while s.find('e0')>0:
              s = s.replace('e0','e')
          while s.find('-0')>0:
              s = s.replace('-0','-')
          return s