Vendor/phpspreadsheet/phpoffice/phpspreadsheet/src/PhpSpreadsheet/Reader/Xls.php
private function readRk()
    {
        $length = self::getUInt2d($this->data, $this->pos + 2);
        $recordData = $this->readRecordData($this->data, $this->pos + 4, $length);

        // move stream pointer to next record
        $this->pos += 4 + $length;

        // offset: 0; size: 2; index to row
        $row = self::getUInt2d($recordData, 0);

        // offset: 2; size: 2; index to column
        $column = self::getUInt2d($recordData, 2);
        $columnString = Coordinate::stringFromColumnIndex($column + 1);

        // Read cell?
        if (($this->getReadFilter() !== null) && $this->getReadFilter()->readCell($columnString, $row + 1, $this->phpSheet->getTitle())) {
            // offset: 4; size: 2; index to XF record
            $xfIndex = self::getUInt2d($recordData, 4);

            // offset: 6; size: 4; RK value
            $rknum = self::getInt4d($recordData, 6);
            $numValue = self::getIEEE754($rknum);

            $cell = $this->phpSheet->getCell($columnString . ($row + 1));
            if (!$this->readDataOnly) {
                // add style information
                $cell->setXfIndex($this->mapCellXfIndex[$xfIndex]);
            }

            // add cell
            $cell->setValueExplicit($numValue, DataType::TYPE_NUMERIC);
        }
    }
private function readRk()
    {
        $length = self::getUInt2d($this->data, $this->pos + 2);
        $recordData = $this->readRecordData($this->data, $this->pos + 4, $length);

        // move stream pointer to next record
        $this->pos += 4 + $length;

        // offset: 0; size: 2; index to row
        $row = self::getUInt2d($recordData, 0);

        // offset: 2; size: 2; index to column
        $column = self::getUInt2d($recordData, 2);
        $columnString = Coordinate::stringFromColumnIndex($column + 1);

        // Read cell?
        if (($this->getReadFilter() !== null) && $this->getReadFilter()->readCell($columnString, $row + 1, $this->phpSheet->getTitle())) {
            // offset: 4; size: 2; index to XF record
            $xfIndex = self::getUInt2d($recordData, 4);

            // offset: 6; size: 4; RK value
            $rknum = self::getInt4d($recordData, 6);
            $numValue = self::getIEEE754($rknum);

            $cell = $this->phpSheet->getCell($columnString . ($row + 1));
            if (!$this->readDataOnly) {
                // add style information
                $cell->setXfIndex($this->mapCellXfIndex[$xfIndex]);
            }

            // add cell
            $cell->setValueExplicit($numValue, DataType::TYPE_NUMERIC);
        }
    }
Read RK record
This record represents a cell that contains an RK value
(encoded integer or floating-point value). If a
floating-point value cannot be encoded to an RK value,
a NUMBER record will be written. This record replaces the
record INTEGER written in BIFF2.

--    "OpenOffice.org's Documentation of the Microsoft
Excel File Format"