This is one of the few exercises you should do without a metronome. You are not aiming for perfect execution, you are evaluating what is.
Set the EQ flat on your bass and amp. If you normally use an overdriven or “hot” sound, set it to clean. You want the most neutral possible tone.
Play an open E, and then play every note on the E string as high as you can go. Go back down. What do you observe about the sound? Obviously, the pitch is getting higher as you go higher up. What else happens?
Go up and down on the other strings. Pay attention to how each area of the neck feels on both your left and right hand. Play every note on the fretboard in as many combinations as you can deal with.
Some things you might notice:
On your left hand, going higher up brings the notes closer together. You will find that you can span a distance longer than a minor third without shifting.
Unless your action is very low, you will notice a difference in how easy it is to press down the strings with the left hand.
On your right hand, going higher up makes the string feel tighter, less like a string and more like a rigid metal rod. You can also observe this phenomenon visually – look at how much you can see an open string vibrate, versus how much you can see on the highest fret. A string fretted as high up as possible hardly appears to be vibrating at all.
You’ll also notice that something is happening with the sound, but perhaps it’s hard to put your finger on without removing the variable of pitch. So now it’s time for the second exercise.