case 'B':
          yy += Math.round((this.maxmin.max - getValue(this.data, 'low', idx)) * this.maxmin.unitY)
          _drawTxt(this.context, xx - Math.floor(len / 2), yy, '▲', this.symbol.font,
            this.symbol.pixel, this.color.red, { y: 'top' })
          break