Something I work on consistently. Many actions of the day or day's prior to the round affect my feel and thus grip pressure.
The scale thing is a tough one for me to judge. The firmness probably changes for the shot at hand. Generally, it is more a result of gripping it as firm as possible (or loosely as possible) without allowing the club to move in the hands AND allowing the wrists its degree of freedom to do what they are supposed to do.
For a drill more than several years ago, an instructor asked me to take my normal grip and extend the club to him so he can grab the clubface. He then took control of the club and moved it at his will, up and down, and/or side to side, and allowed me to respond to his movement without losing my grip. After finally giving up control to him and responding to his movement with my grip intact, he said that is what I should feel with respect to the relationship of the hands and wrists.
whether this drill has its merit as an instructional drill for others, dunno, but i got the point.