An apparatus for cleaning and cooling a liquor nozzle, the nozzle including at least a liquor tube for feeding liquor and chemicals into a furnace of a recovery boiler. The method includes performing by the control module, estimating a steering load gain; estimating a steering load hysteresis; and determining friction based on the steering load gain, the steering load hysteresis, and a reference model. Then, a flatness calculating method is selected according to a position of the site to be evaluated and flatness in the wafer surface is acquired.