The present invention provides methods to maintain selectivity to ethanol from syngas during mixed-alcohol synthesis when methanol is being recycled. The cavity positioning tool includes at least one blunt arm pivotally coupled to the housing. The second processor is configured to transmit a first signal based on the command, and the first signal indicates a compliant command. The scale plate has an air-guiding hole so that a cylinder hole of the cylinder is communicated with the air-guiding hole. An application programming interface is used to facilitate synchronization, and includes a set search method, a search function template method, and a clear search method.