Comment by Theodores

It was a 1 x 9 print head and you could get 132 characters per line as well as the normal 80, plus variants such as 40 and 66 characters per line, where things must have been doubled up with the motor running at the same pitch, hence the 12x9 you refer to.

I only became familiar with the later FX-80, which was the same but different. I managed to get logos printed along with neat boxes around information from the extra characters it had in PCL.

I am sure NLQ was a selling point of the FX-80 but I would like to see how good it was on the MX-80. At the time printers from Epson, HP and Canon were miracles of engineering, more advanced than the computers they were connected to.