Yes, senses are inherently subjective. Yes, reading a scale with your eyes can throw off the result. There is an accepted protocol on how to read a meniscus in a graduated cylinder for this reason or any scale for that matter.
When you say I believe I turned off the oven, you are subjectively recalling something. You aren't looking at the oven, you're remembering it. You aren't checking that it's off. You're saying that to the best of my memory, I turned it off. "I'm pretty sure." That is subjective.