The plunger in the center of the cam chain adjusting bolt "pulses" in and out as the motor turns over. That would explain you finding it in different spots the two times you looked at it. The motor was probably in a different spot in it's rotation each time. The plunger is spring-loaded and pushes a big rubber/metal "shoe" against the back run of the chain to take up it's slack. But, like any chain, the cam chain stretches unevenly, developing "high" and "low" spots, or loose and tight sections. When a tight spot runs by the tensioner, it pushes the plunger out, when a looser spot goes by, it allows the plunger to move back in.
Because of this in-out movement, one of the easiest ways to check and/or adjust the tension is while the engine sits there idling. You want to tighten the adjuster up so you have a small amount of in-out movement, maybe 1 to 2mm. No movement means you've set it too tight and any more than the amount mentioned means it's too loose. If it's really loose, the chain will make noise like loose valves.