One obvious problem with the obtrusive pro- peller meter is that the bearings wear out and have to be replaced. Additionally, as the bearings go from new to old, the accuracy goes from fair to poor. Another problem with the propeller meter is that it is prone to magnetic pickup resulting in bad signals and questionable flow read- ings. Finally, the size of these massive pro- pellers makes maintenance a major under- taking. The Accusonic multipl

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