Insoric real power dyno?

I have perfect stretch of road very close to my workshop for testing but its not completely flat it has very slight incline will this be a problem or can i use for

its about comparable data

if the stock vs tuned run is done on same road, same inaccuracy % will be present in both runs and thus cancel eachother out

If I understood you right, this is what I meant too. You probably don´t get exact hp, but you have the difference that made tune to stock. Because the car runs the flat road faster and the small pitch faster. But don´t compare flat run with the small pitch run.