The invention relates to an image support medium for creation of an aesthetic image that is a work or object for display. The plant cover has a heat shrinkable bonding material which can be heat shrunk to secure the plant cover about the pot. The new hub design for a turbine equipped with three blades has been modeled using modified FAST code and has shown significant advantages over present three-bladed turbines with fixed hubs in reducing loads on the blades, tower, main shaft and bearings. Accordingly, any specific mechanism for only the cleaning purpose is not necessary and the construction of the apparatus can be made simple. The apparatus for controlling the operation of the compressor includes: a triac electrically connected to the compressor; and a controller for controlling a turn-on duration of the triac on the basis of a voltage value of an alternating current power applied to the compressor and a predetermined reference voltage value. An indicator representative of at least one cost of the range of costs is displayed.