[support] Drupal 6 computed field

[Roger]

After following the README.txt in the Computed Fields module.
---====---
 Computed Code:
$node_field[0]['value'] =
$node->field_fieldname1[0]['value'] +
$node->field_fieldname2[0]['value'];

- Check 'Display this field'

- Display Format:
$display = '$' . $node_field_item['value'];

- Check 'Store using the database settings below'

- Data Type: float

- Data Length: 10,2

- Default Value: 0.00

- Check 'Not NULL'

- Check 'Sortable'
---====----
 I set up one content type "Calculate Total" containing one calculated
field which displays $0. This has me puzzled as there are 6 values each
in field_fieldname1 and field_fieldname2.

What code should I be using to display the sum of the 2 fields. 
and display fieldname1 \ 1.101

I can do the calculation in mysql but not in drupal.
I feel there should be more code but haven't a clue what to look for or
how to implement it.

Thanks in advance
Roger