Gadgetbridge/app/src/main/res/layout/fragment_sleepchart.xml

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context="nodomain.freeyourgadget.gadgetbridge.activities.charts.ChartsActivity$PlaceholderFragment"
    android:orientation="vertical">

    <com.github.mikephil.charting.charts.PieChart
        android:id="@+id/sleepchart_pie_light_deep"
        android:layout_width="fill_parent"
        android:layout_height="fill_parent"
        android:layout_weight="20"></com.github.mikephil.charting.charts.PieChart>

    <com.github.mikephil.charting.charts.LineChart
        android:id="@+id/sleepchart"
        android:layout_width="fill_parent"
        android:layout_height="fill_parent"

        android:layout_weight="20" />

</LinearLayout>