Test.xaml

<UserControl x:Class="VECTO3GUI2020.Test"
             xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
             xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
             xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006" 
             xmlns:d="http://schemas.microsoft.com/expression/blend/2008" 
             xmlns:local="clr-namespace:VECTO3GUI2020"
             xmlns:customControls="clr-namespace:VECTO3GUI2020.Views.Multistage.CustomControls"
             xmlns:helper="clr-namespace:VECTO3GUI2020.Helper"
             mc:Ignorable="d" 
             d:DesignHeight="450" d:DesignWidth="800" d:DataContext="{d:DesignInstance local:TestViewModel }">

    <Grid>

        <!--https://www.thomasclaudiushuber.com/2008/01/10/bind-to-methods-with-objectdataprovider/-->
        <StackPanel>
            <!--<customControls:MultiStageParameter Content="{Binding ConvertedSI}" DummyContent="{Binding Source={StaticResource milimeterDummy}}"/>
            <customControls:MultiStageParameter Content="{Binding ConvertedSI1}" DummyContent="{Binding Source={StaticResource milimeterDummy}}"/>
            <customControls:MultiStageParameter Content="{Binding Meter}"/>-->
            <customControls:MultiStageParameter Mode="COMBOBOX" Content="{Binding HeatPumpMode}" EditingEnabled="{Binding enabled}" ListItems="{Binding HeatPumpModeListItems}"></customControls:MultiStageParameter>
            <!--<customControls:MultiStageParameter Mode="COMBOBOX" Content="{Binding HeatPumpMode2}" EditingEnabled="{Binding enabled}"></customControls:MultiStageParameter>-->
            <!--<customControls:MultiStageParameter Mode="TEXTBOX" Content="{Binding TestString, ValidatesOnExceptions=True}"></customControls:MultiStageParameter>-->
        </StackPanel>
    </Grid>
</UserControl>