What is the difference between "2B" and "HB" pencil? | Yahoo Answers

What is the difference between "2B" and "HB" pencil? | Yahoo Answers:



Pencil
lead is made of graphite (a form of carbon) and clay. The hardness is
adjusted by different composition of the two. More graphite means
softer pencil. More clay means harder pencil.



2B is soft

HB is medium hard

2H is hard



2B is darker, easily smear hence messier. HB is more likely to leave an indentation on the paper and harder to erase.



Graphite conducts electricity. Many years ago when automated scoring of
multiple choice tests was first introduced, the answer sheet reader
actually read the sheet electrically by detecting the presence of
graphite on the paper. Back then 2B pencils was standard for testing
because more graphite means better reading.



Nowadays, optical sensor is so cheap and it is probably more accurate
than electrical sensor. The conducting property of graphite is probably
not a concern anymore. Since the blackness and reflective attribute of
2B and HB pencils are different, which to use really depends on how the
optical reader is calibrated to use. So you should follow the
instructions on the answer sheet in order to minimize the misreading of
your answers. When in doubt, bring both.