The so-called 'lowest mark' is actually the mark at the 25th percentile. There aren't stats available for marks below that range so they're impossible to scale accurately. I'm sure I explained this somewhere on the LazSeeker site.
Remember that you can't compare aligned HSC marks between courses, so an 80% in 4u maths is nothing like an 80% in biology etc. However, you CAN compare scaled marks - a scaled mark of 80 in 4u maths is exactly the same as a scaled mark of 80 in biology (they will have very different corresponding aligned HSC marks).
Remember that you can't compare aligned HSC marks between courses, so an 80% in 4u maths is nothing like an 80% in biology etc. However, you CAN compare scaled marks - a scaled mark of 80 in 4u maths is exactly the same as a scaled mark of 80 in biology (they will have very different corresponding aligned HSC marks).