[wrp]

A confusing thing about pencil lead for test marking is that while a #2/HB hardness is usually specified, there were specially marketed pencils that were actually softer. The pencils and leads were generically branded as "mark sense". They had a higher graphite content to improve electrical conductivity, but which also made the leads softer. (Scanning machines initially used electrodes, then switched to optical sensors.) I haven't been able to test many samples, but I think "mark sense" pencils were about 4B.