This whole post reminds me of the post periodic test flight.
I used to rig the Flight Controls and make it as straight as I can.
The Test Pilot said they test to see how straight it is by flying at a certain alt, certain AOA (level flight), certain speed and let go of the stick.
The jet should naturally roll, the time it take to start rolling determines how "straight" Flt Ctrls are. If it rolls too fast (I believe under 2 min) we had to re-rig the Flt Ctrls.
My personal best was 4.5 mins before it started to roll. We're talking over 20year old jet.