You should measure chain slack by the amount it moves perpendicular to the chain, not vertically from the ground. The tape measure should be at an angle.
I keep some small round magnets stuck to the side of my frame. I stick them on the chain to indicate the tightest spot. You just have to remember to remove them from the chain once done. I also put a small vinyl decal on the swing arm to indicate chain mid-point so I don't have to remeasure each time.
The magnets are also great when lubing chain to indicate your starting/ending point as you're spinning the wheel and spraying lube.
Last edited by brock29609; 10-10-2018 at 12:56 PM.