void ChartModel::appendData(double leftEye)
{
    if (leftEye != leftEye)
        qDebug() << "invalid leftEye - NAN";

    int vecSize = vec_.size();
    if (vecSize == m_xMax) {
//         for (int i = 0; i < vecSize; ++i) {
//             vec_.removeAt(i);
//         }
        vec_.clear();
        vecSize = vec_.size();
        emit modelSizeChanged();
    }

    beginInsertRows(QModelIndex(), vecSize, vecSize+1);

    double xVal = vec_.size();
    QList<double> coordinates = {xVal, leftEye};
    vec_.push_back(coordinates);

    endInsertRows();
//     qDebug() << m_xMin << m_xMax << vec_.size() << xVal << leftEye;
}