I shall date myself by saying my last experience on the Chinook was with the mature C Model having cut my baby teeth on the earliest A Models with the fixed landing gear (one of them I learned to fly Chinooks in is now in the Fort Rucker Museum).
In my time the Speed Trim system (being called DASH) by some here.....consisted of electrical servos that would controlled by air pressure created through the Pitot Static system with the changes in airspeed.
The system was switched ON by Checklist....and once turned own did its own thing....with Cockpit Instrument Panel Indicators (one for each Rotor Head) showing the position of the Servos. In the event of a failure of the automatic system there was a Manual Option that required constant input by the Crew and also provide a means to manually retract the Speed Trim Servos before Landing.
If the Crew put the Trim into Manual and forgot to manually retract the Servos....an extraordinary stress was applied to the Aft Vertical Shaft on the Aft Transmission and also caused an unusual landing attitude.
The purpose of that system was to level the fuselage during cruise flight and eliminate drag.
Lots have been said about the "Positive Stick Gradient" requirement imposed by the Army and FAA (the S-76 was labored with similar problems) but in real life use....most Pilots cannot identify when that system is working or not unless they see a Instrument Indication to that effect.
Monkey Memory accrues from comparing a cyclic stick position to Pitch Attitude/Air Speed and then moving the Cyclic to achieve the result desired....then repeated throughout the flight.