AdditionValueConverter.cs

using System;
using System.Windows.Data;
using System.Globalization;

namespace CodeBlockEndTag
{
    internal class AdditionValueConverter : IValueConverter
    {
        public object Convert(object value, Type targetType, object parameter, CultureInfo culture)
        {
            return System.Convert.ToDouble(value) + System.Convert.ToDouble(parameter);
        }

        public object ConvertBack(object value, Type targetType, object parameter, CultureInfo culture)
        {
            return System.Convert.ToDouble(value) - System.Convert.ToDouble(parameter);
        }
    }
}