def calc_dt_before_1961(y)
      t = y - 1950
      dt  = 29.07      + \
           ( 0.407     + \
           (-1 / 233.0 + \
           ( 1 / 2547.0) \
           * t) * t) * t
      return dt
    rescue => e
      raise
    end
def calc_dt_before_1961(y)
      t = y - 1950
      dt  = 29.07      + \
           ( 0.407     + \
           (-1 / 233.0 + \
           ( 1 / 2547.0) \
           * t) * t) * t
      return dt
    rescue => e
      raise
    end
=========================================================================
 deltaT (1941 <= year && year < 1961)

 @param:  y   (Year coefficient for deltaT calculation)
 @return: dt  (sec)
=========================================================================