Here are three blocks of shade with the same pressure from different pencils:
You can’t see the difference. In order to make the tone differences obvious you have to press down on the 6B, press a little on the 4B and only press lightly with the 2B:
A record of my 'picture a day' challenge
Here are three blocks of shade with the same pressure from different pencils:
You can’t see the difference. In order to make the tone differences obvious you have to press down on the 6B, press a little on the 4B and only press lightly with the 2B: