the best tool to ANY engineer, steam or diesel, is the one that he is sitting on....his OWN "hind end" - You can feel what the train is doing by what you are feeling in the seat. Its hard concept to explain, but very easy to understand once you can feel it and understand it.
Those doubleheaded steam locos would even more so be felt by the seat of their pants. Thats how to tell whats going on with the rest of the train and the other power, if you didn't hear a radio call or a whistle blow. If say the loco is pushing on the back - if the front coupler of the loco you are running gets the slack pulled out of it, and you feel the train tug your engine, that means (in a nutshell) that the train is being stretched, which more than likely means the engine on the front is pulling for power. Conversely, if the engine you are on in the back "runs into" the train and the front of the train seems to be slowing down as the engine you were on was going slightly faster, that basically means that the train is slowing down. Of course, grades and hills all play into this, but imagine a totally flat run to get to understand the concept.
The engineer should be able to see or feel what a train is going before seeing it in the speedo. Also, most (not all) engineers don't particularly use their gauges as much as you might think - especially the air gauges. Each train handles differently, so if you make a predescribed brake reduction at a certain location, one day it might be exactly what you want, the next day, not enough brakes, the next day too much brakes. You have an idea of what to do and where to do it, but you have to constantly adjust because of how the train is handling. Also, when running slow, or drilling (shifting cars around in a yard or an industry) most (again, can't say all) engineers don't even look at their "dash" but rather down at the ground next to the cab. After a while you get a really good feel for speed, and will only occasionally glace up at your speedo. It really doesn't matter if you have 1 loco or 10 locos.
On the RR, "believe nothing you hear and only half of what you see"
John, aka "JTGSHU" passed away on August 26, 2013. We honor his memory and his devotion to railroading at railroad.net.