An umbrella stand includes a housing and an operation mechanism mounted on the housing. Each VAD measures the spectral energy in a sub-band, compares the spectral energy to a first threshold, and produces an output signal representative of whether or not the first threshold is exceeded. x is normalized with a normalization factor calculated for the interval into which x falls to obtain a normalized value x within a normalized range. The diverter is located in a passageway of the shunt tube to divert at least part of the flow. In this way, the test case manager directs the test units to carry out the test case actions.