Not to take away any of Woz's brilliantness, but coding the 6502 in hex was something many of us did every day in the 80's. He's right that branches are a tad tricky, but the number of instructions you usually use are few enough to remember the hex codes(and number of cycles) for along with the various hardware registers(CIAS, VIC-II and SID mostly for me) and bits within those registers.