I've never learned a good easy way to measure my primary chain deflection. It looks easy in the manuals but that's because they have the primary opened up for easy visibility and access to the chain. Working through that little chain inspection window is not nearly as easy as the pictures show. I'm getting ready for fluid change and adjusting the primary chain and think I'll try using a long screw driver, making a sharpie mark where the screwdriver blade is at the bottom edge on the inspection window just touching the chain at the top middle; then pressing the screwdriver up until the chain is fully deflected and making another sharpie mark on the screwdriver blade at the bottom edge of the inspection window. The measurement between the two marks on the screwdriver is the chain deflection. Probably someone has an easier way to measure chain deflection and I'd appreciate knowing how they do it.