The above image is a close up of the first word in the 3rd line (and). You will note the backlit downward stroke of the letter 'd'. I have done a little enhancement to bring up the numbers so that they're more readily visible. Of note is the fact that these numbers are aligned with the inked area, this was part of the technique whereby inked letters were laid down first and then the shape of the letters were used as guidelines within which the micro content would be inserted. My estimation is that these micro numbers are in the range of .5 to .7 mm.