Hello everybody ...
When you retrieve data and put in the GRID
only recover 'n_meta' and 'n_m00'
It is possible that when retrieving the data to make an operation using the renderer and burn in 'n_porc' ===> (n_meta / n_m00) * 100

Code:
function pctAvance(val){
        return val;
    }
 
var Grid = new Ext.grid.EditorGridPanel({
        store: Inicio,
title:'Actividades',
        ....
        columns: [
      {header: "Programado",dataIndex: 'n_meta', width: 70, align: 'right'},
{header: "Ejecutado",dataIndex: 'n_m00', width: 70, align: 'right'},
{header: "%",dataIndex: 'n_porc',  renderer: pctAvance, width: 70, align: 'right'}]