I bought an MRC Tech-4-220 power pack for my N-scale layout. It's cool, allowing me for the first time to operate my locomotive at less than 100 mph. Now, the 220 has a "momentum" control and a "brake" control, which supposedly allow more realistic train control. The brake is a no-brainer. It lets you stop the train when and where you want. It's the momentum control that I have a question about. I've found three ways to use it. Let's say that I want to move my GP-38 through the yard at 20 mph. 1. With the momentum switch off, I adjust the throttle to the 20 mph setting and the train almost instantly reaches that speed. Fast response, but not like the prototype. 2. With the momentum switch on, I adjust the throttle to the 20 mph setting. The train only starts to move after 5 seconds, or so. It begins to creep imperceptably at first, then VERY slowly accelerates to 20 mph, taking 20 or 30 seconds to get up to speed. 3. With the momentum switch on, I adjust the throttle to the 150 mph setting. I leave it there until the train begins to move, after about a second. Then I quickly lower the throttle to the 20 mph setting, and the train quickly and smoothly accelerates to to 20 mph, taking only three or for seconds to reach that speed. My question: How would an engineer on a prototype GP-38 handle his/her throttle? Do these locomotives require operation more like scenario 2, or 3? Any opinions?