User generated variations / different machines

In my gym, there are four different leg press machines, and in another gym I train regularily, there are yet another two leg presses from different manufacturers. They might have a different resistance with the same weight because of mechanics, angle or weight of the sled, etc.  Still, they are still all under the heading "leg press". The same goes with several pulleys; on one machine the same weight feels heavier than on another. 

This creates a problem as the AI won't know whether I made more reps with a certain weight than last time because I am stronger, or because I used a different machine. 

One solution would be to let the user create variations of excercises for each different machine, but the AI would treat them as the same exercise when it cames to progression. So, there would be user generated "leg press" for brand A leg press, another for brand B, and so on. However, the AI would treat all of them as "leg press". When the user progresses 1% in one variation, that would tranfer to all of the variations.