Can you sum custom field values into another custom field?

[Thomas Kakutani]

I am trying to sum 3 number custom field into a "TOTAL" custom field. I saw this (https://help.trello.com/article/1161-custom-field-arithmetic) article, but after changing it to my custom field titles it was not summing. I think because this article is put out by Trello there is a way to do this, but I am not quite sure where to go with this. 

[Felix · Accepted solution]

You can sum number fields, just make sure that you keep the syntax as in the help document. Here's an example of 2 rules to sum up 2 fields:

Note that the field name in the is prefixed with {{% and postfixed with }}, so a field with name "abc" would be {{%abc}}