PHPExcel - break links to other sheets

gistfile1.php

    // Replace calculated values with static data. From A to H from 1 to 70
    function breakExcelLinksInSheet( $sheet ){

        $labels = array( 'A', 'B', 'C', 'D', 'E', 'F', 'G', 'H' );

        foreach( $labels as $label ){
            for( $i = 1; $i < 70; $i++ ){

                $val = $sheet->getCell( $label.$i );
                //for incorrect formulas take old value
                if( ( substr( $val, 0, 1 ) === '=' ) && ( strlen( $val ) > 1)){
                    $value = $sheet->getCell( $label.$i )->getOldCalculatedValue();
                    $sheet->setCellValue( $label.$i, $value );
                }
            }
        }

    }