Custom field that is a calculated field off of other completed fields

Custom field that is a calculated field off of other completed fields

We score each Potential as we develop the opportunity prior to bid.  The score is comprised of the sum of a series of individual scores.  We have created fields for each of the individual scores.  These fields contain a drop down pick list with the options being 0,1,2,3..10

I would like to create a calculated field (not manually editable) based on the sum of the fields contain the individual scores.  There does not appear to be a cell based function to access the value of another field automatically.  Any ideas?

INdividual Score A - 4
individual Score B - 7

Total Score - 11

How do I create the Total Score field to sum Score A and Score B automatically.