Athearn Blue Box DD40 tractive effort and horsepower testing

How to figure out how much pulling power does an HO scale locomotive have and how is it measured and what does the measurement mean in the real world. We are going to label horsepower as how many cars that weigh 4.5oz. pull up a 4% grade using the formula 1oz. of pulling power is equal to 3.8 cars. This is what we will call horsepower, not what the actual real horsepower measurement would be, but this formula is close enough and gives us useful information for our database that records all the info about our HO scale locomotives. Testing the tractive effort of the Athearn Blue Box single motor vs. dual motor vs. SD70M vs. SDP40 vs. 2 U28B and 2 AHM GP18.