void ChartModel::appendData(double leftEye)
{
    int const vecSize = vec_.size();
    qDebug() << "vecSize = " << vecSize;

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

    double const xVal = vec_.size();
    double const yVal = leftEye;
    vec_.append(qMakePair<double, double>(xVal, yVal));

    if (xVal > 30) {
        set_xMin(xVal - 30);
        set_xMax(xVal);
    } else {
        set_xMin(0);
        set_xMax(30);
    }

    endInsertRows();
}