Shows how to set up a Participants Database field that keeps a total of several other fields.

pdb-total-field-handler.php

<?php
/*
  Plugin Name: Participants Database Total Field
  Description: Maintains a total of several fields
 */

// this updates the total when the record is updated
add_filter( 'pdb-before_submit_update', 'xnau_update_total_field' );

/**
 * updates the total field
 *
 * @param array $record the submitted record data
 * @return array the data to store
 */
function xnau_update_total_field ( $record )
{
  // set this up to list the fields to sum
  // must be numeric!
  $fields_to_total = array('numeric_1','numeric_2');
  
  // name of the total field
  // should be numeric field
  $total_field = 'numeric_sum';
  
  // calculate the total
  $total = 0;
  foreach ( $fields_to_total as $field ) {
    $total += $record[$field];
  }
  
  // place the total in the data array
  $record[$total_field] = $total;
  
  // return the record data to be saved
  return $record;
}

There is no error checking of any kind, so be careful to use the correct field names, also they must be numeric in order for the totaling to work.

can you explain where this code goes, so i',ve tried on the theme funcions and in separate file on the plugin folder and no way.Thx in advance

This code is a plugin, take a look at this article which explains how to install it:

How to Install a WordPress Plugin from a Gist