[chaley]

Your problem comes from confusing constants with field (column) values. The string '#chapters' is a constant. It always has the value '#chapters', which as you can see is not a number. To get the value of a metadata field you use the 'field' function. This function takes the name of the field as its first argument. This argument is normally a constant, but certainly does not need to be.

Using the above, your first program would become:

program:divide(field('#words'), field('#chapters'))

This program can produce floating point output. For that reason you might want to use

program: format_number(divide(field('#words'), field('#chapters')), '{0:5.0f}')

Finally, if there is any chance that the #chapters field is empty (zero) then you need to test for that before doing the divide. That is more complicated, requiring something like the following:

program: 
# Get the value of the chapters field so we can use it more easily
chapters = raw_field('#chapters');

# Check if chapters is zero. If it is then put  the empty string into the variable notIsZero
notIsZero = cmp(chapters, 0, 'yes', '', 'yes');

# Ensure that the chapters variable contains a non-zero number. We need this because the divide will happen
# even though we will throw the value away
chapters = test(notIsZero, chapters, '1');

# Return the result of the divide if notIsZero contains the non-empty string, otherwise return the empty string
test(notIsZero,  format_number(divide(field('#words'), chapters), '{0:5.0f}'), '')