Plumbing and Static Sources

As previously said - look in the manual and TC for directions from the manufacturer as to what source to use. Usually they will specify a source for the ASI system as the placard limits are in IAS using those sources. I've often found they will specify on for the altimeter too though as UH says it doesn't matter much for the altimeter. Paul Bickle and Dick Schraeder's tests usually found that the most accurate static sources are ones well aft on the fuselage sides so those should be used for varios. Static sources on the multi probe are probably very accurate too. If you have both aft fuselage statics and a multi probe you could use the fuselage ones for the mechanical vario and the multi probe for the electronic vario so that the two don't suffer from interference.