Hi,
To calculate the aerobic threshold ,the correct way, is to do it in a place that is controlled and where you are able to compare with future or previous efforts .
If you want to use incline , use a treadmill ( the best option )
To calculate the drift , you need to warm up and make it stabilise at a target heart rate,
the data you put on the description, doesn’t have a reference to that, interpretation of the data , you should mention that.
The reason why it’s done on a track or treadmill , controlled environment, it’s to take as many variables that can affect the test result, to do a better test , the incline should be the same , the path should be the same , the speed should be constant, etc .
I hope I could be helpful with my answer
Cheers,
Pedro Carvalho