private void load_exchange_rates_from_settings()
{
string s_exchange_rates = Properties.Settings.Default.exchange_rates;
byte[] b = System.Convert.FromBase64String(s_exchange_rates);
MemoryStream memoryStream = new MemoryStream(b);
BinaryFormatter binaryFormatter = new BinaryFormatter();
object o = binaryFormatter.Deserialize(memoryStream);
exchange_rates = (Dictionary<string, exchange_rate>)o;
}