Leak Down Procedure (Pic Heavy)

I checked the motor on my very low hours go-devil mud motor (v-twin vanguard briggs) same deal it's saying 18%! That gauge set has got to be goofy! It's saying that my 273,my merc & my mud motor are all worn out! It's gotta be the gauge set! I havnt had eny thing ever read better than 18%! None of the them burn oil have great power. As for the 60 hp merc (or any 2 stroke) ring seal is a MAJOR factor in how they will run mainly @ idle. Without good ring seal it will not have the power/vacuum to draw in the next air/fuel charge. Until the Rpm is higher to cover it up. Like I'm thinking my gauge set has got to be somthin wrong with it. The big gauge when set is 25-30 psi it seems alot lower than any other set I've seen before. So it's putting in 25-30 psi & loseing 18-20% of that. The 273 is a year old with apx 3000 miles on it & runs great!