forgive me if this is too chemistry. I am playing around with pencils, writing and art pencils, to teach some kids about resistance and resistivity in a fun way, or so I believe. I get about 200 Ohms for a standard full length HB (whatever that means) pencil. I have some charcoal art pencils and a range of "HX" or "YH" writing pencils where X & Y are a number or letters. my DMM is dead right now but hope to see a measurable difference when "H" is varied. anyone know; a) how the _H_ labelling system works and what it means. I figured which ones are dark and light and observe a different hardness but what is the logic of the labelling system. b) how _H_ value relates to the atomic structure of the pencil in order to explain the different resistivity's. obviously theory describing conduction electrons in metals and semi-conductors is useless here. c) are there other systems than _H_ how is graphite related to charcoal properties wise. I did get a data sheet from a pencil manufacturer but it zero info on micro-structure. thanks any ideas.