## Calculate a new field's values based on two others

        $t->calc($Sub)              ## Run $Sub for each row, with 
                                    ##  fields bound to local vars

        $t->calc($Sub,  $Sel)           ## Use these row nums
        $t->calc($Sub, undef, $Fields)  ## Use only these fields

        my $Col = $t->calc($Sub)    ## Gather return vals in vector

o o o
        ## Example 2: Create empty column; fill fields 1 by 1

        $t->col('PersonID');
        $t->calc(sub{no strict 'vars'; $PersonID = "$Last$First"});