function toDate(serial) {
    if (serial < 0) {
        throw FormulaError.VALUE;
    }
    if (serial <= 60) {
        return new Date(d1900.getTime() + (serial - 1) * 86400000);
    }
    return new Date(d1900.getTime() + (serial - 2) * 86400000);
}
Parse an excel serial number to UTC date.
@param serial
@returns {Date}