C# show if numbers in listbox getting bigger or smaller

Question

I have a listbox that numbers are added each 10 seconds. Numbers such as ( -5, -4, -3, -2, 0, 1, 3, 5, 6, 3, 2)

New numbers added after the number 2. I want to show that if the numbers are increasing from -5 to 2, then the outcome would be positive. However, lets say if the numbers are decreasing, then it would have a outcome of negative. In the parenthesis you can see the numbers are increasing from -5 to 2, so the outcome should be positive. How do I express that programmatically.

                foreach(decimal item in listBox1.Items)
                {
                   if (listBox1.Items.Count -1 > listBox1.Items.Count -2) // this line is where i am confused on how to do. it has to consider all numbers in listbox and see if the direction of the numbers is going positive or negative. 
                    {
                        MessageBox.Show("numbers are increasing OUTPUT: POSITIVE");
                    }
                }