Whoops!, thanks for the jockey wheel advice re calibration, shows how useful this forum is, never too old to learn!
I have just looked at the Al-ko details in my pack ( I did not know I had this) & decided that I will calibrate it myself using a set of scales & avoid the maths, that is if I decide I need to know the exact figure that it equates to.
My point is, that as long as you have made a note of a reading on the jockey wheel gauge that gives you a good towing balance, quickly found after a couple of trips, then that reading is what you should always use, mine, out of coincidence for my yeti, happens to be the 70/75 mark.