Epson Apex-80 - Manual (Page 56)

Each NLQ character definition requires 36 data numbers. Therefore,
each vertical column must be divided into three sections for the
calculation of data numbers. The process is not difficult once you get
some practice using it.
Figure 5-6 shows a single column to make clear how the data
numbers are calculated. Notice that in designing NLQ characters
circles are used instead of dots to make it easier to keep track of
overlapping dots.
Figure 5-6.
Data numbers for one column
To calculate the data numbers for this column, you see which dots
are used in the top group (the top eight positions) and add their values
together. Then you go down to the middle group (the next eight
User-defined Characters 5.9