private void on_entry_fall_value_changed(object o, EventArgs args)
{
if(Util.IsNumber(entry_fall_value.Text.ToString(), true)){
entryFall = entry_fall_value.Text.ToString();
button_accept.Sensitive = true;
} else {
button_accept.Sensitive = false;
//entry_fall_value.Text = "";
//entry_fall_value.Text = entryFall;
}
}