Hey Edge, I just pulled out a 15/6 APC and compared the two and the 15/6 is obviously flatter so I believe the 15/8 is a 15/8. I tached it outdoors. I've only used this tach on Saito and OS 4 strokes and never reached over 9300 r.p.m.s on these engines so I was stunned when it first read 9800. Then when it went past 10,000r.p.ms I knew the tach was in error and opened the brand new one with the same results. I wonder if anyone else has had this happen with Globee Tachs. Anyway I didn't get a chance to try the 16/8 due to hurricane preps. If this stuff happens again I will buy a different brand tach. I am also using a Slimline Pitts muffler that is designed for the YS 91 but was assured by YS performance that it was o.k. to use. When I first started running 4 strokes, alot of guys using them used the heaviest props they could find and said they liked the "flywheel effect" which gave them a better idle. I've been going by this for years but don't really know if it makes a difference. I am going to try running both props and take readings again as soon as the weather clears.