A method for monitoring a plurality of rack systems is provided, which includes the following steps. The heap structure is implemented using a radix value for grouping the N TS values into a number of groups. The reserve tank and the legs are integrally formed as a unitary structure. Thus, when single-crystal sapphire is obtained by growth from a melt of aluminum oxide, formation of a protrusion in the tail portion of the single-crystal sapphire is more effectively inhibited. First gate stack-forming layer includes a non-conformal layer of metal gate-forming material which is directionally deposited to form a thinned break portion just below the lateral overhang portion. In one specific embodiment, the color variation is reduced, while in another embodiment the color variation is increased to enhance pattern contrast.