Hawkshot99 have a good explanation of how most hydro units work. My concern with your Trimstar is that you must hold the speed controls in the same place to maintain constant speed. Am I right about this? Hawkshot99 is right about setting the maximum speed with the control lever, and then letting the spring control keep the setting against that control. Any slower speed is attained through pulling back on the controls. This means that the operator is not holding the controls at one position to maintain constant speed. I've not driven a Trimstar, but it appears to me that you must roll the handles to a given position, hold them there, to maintain speed. In other words, there is no stop to push against to keep a constant speed. Every time you turn, you must return to a similar position as before. With the system Exmark system (and many others), the control is returned to the same position as before the turn. I have a ZTR, and it too has no stop to push against for the same speed. Control levers must be held at the same position to hold constant speed. I would think the motions of the small w/b would be difficult to hold at constant speed -- both would have to be turned and held at the same position all the time. This would mean no one-handed operation while working under trees, around bushes, etc. Do I understand TrimStar controls correctly?