There is no such thing as a "properly tuned bar".
You take your bar, any bar, and find the stall point by sheeting the kite, and then you trim either with the depower or knot settings, to find your personal liking.
Most often different sizes even from the same brand has a tad different trim, so if you use the same bar for several sizes, you either need to change the depower when changing kite, or you have to change the bridle lines at the kite if you want the exact same feel for different sizes.
That is all there is to it - find each kitesize's stall point, and work from there.
Using your personal trim liking of course.
Some freestylers, or beginners, want to be able to pull the bar in fully, without backstalling.
Others want the kite to backstall when bar quite far away.
I always ride so my kite backstalls quite early, as I want my bars working point to be quite far away from me, so I hardly never pull the bar in fully - only when I deliberately want the kite to stall deeper into the window, during bottom turns t.ex.
You can not measure a "correct tuned" bar - you can only find a correctly tuned bar for your personal liking and for a given kitesize.
If using the same bar, adjust at the kite if you dont want to bother/remember using the depower trim.
Most experienced riders start with kite fully depowered when launching, and then power it up to the pleasant trim in 10 seconds when riding, takes no time when you are experienced, to find this setting.