A service method of gas appliances includes: Detecting the gas appliances at the client ends to generate detecting signals. The directed acyclic graph can have a set of alteration nodes that collectively define a joint probability. A first forwarding path can forward the sets of condition information from the first processing circuitry to a predetermined pipeline stage of a processing pipeline of the second processing circuitry. The tool may further include first and second levers pivotally mounted to the inner member at respective pivot axes, and each of the levers having a gripping portion.