It would vary, depending if you were on a straight and level grade, on a descending grade, or on an uphill grade, or whether a portion of your long train was strung out over a distant hump in the trackage, about to crest the hump of the track grade, where the rear end slack could suddenly "run in" bunching up the couplers. Or whether you were in a single loco, multiple loco consist, pulling 10 railcars, or pulling 100 railcars. A notch 1 position (for example) would result in many different varied speed physics, traction motor voltage and amperage, on different grades, and in different weather conditions. An engineer would develop a sixth sense on how the consist physics is exactly handling on that particular track grade, "feeling" what notch to apply, or reduce, or where to notch it up, or notch it down, or to coast rolling along in notch zero, or whether to apply dynamic braking, train braking, or independent braking.