Graphite pencil hardness grading.
https://diqn32j8nouaz.cloudfront.net...s_fullsize.jpg
Previously:
https://www.homemadetools.net/forum/...142#post211056
https://www.homemadetools.net/forum/...501#post122786
https://www.homemadetools.net/forum/...901#post194585
https://www.homemadetools.net/forum/...008#post191263
https://www.homemadetools.net/forum/...1199#post73924
