Each cylinder chuffs twice during a single revolution of the driver, once for the front stroke and once for the back stroke. The main crank on the other side of the locomotive if 90 degrees either forward or lagging the crank on the engineer's side, depending on the railroad's preferences. So it's valve is halfway through its travel between the two ports, and it won't allow a chuff until the right-hand side valve is itself halfway through a cycle. The net effect is a staccato of chuffs separated by even time gaps, and they should be distinguishable as four separate chuffs, four per revolution of any one driver on either side of the engine.
You can rehearse the 'beat' in your mind by watching when the main crank comes to a defined point, say bottom dead center, and begining to count with a changing pace until you can maintain a synchronized beat in your head to match four beats with the crank returning each time to bottom dead center. Once you learn to do this, you'll have a hard time not rolling your eyes at all the older 16 mm steamer film now on video and DVD when you can clearly tell it is dubbed, and not with a steamer moving at the same pace.
For those with a Tsunami decoder, CV116 is the one you want to set the chuff rate. It unfortunately changes a bit with a cold locomotive versus one that has been warmed with use for maybe 10 minutes. But you should get the engine moving at speed step 10, let it warm up a bit on a loop, and then enter Ops Mode, dial in CV116, and I would start with a value near 145 and work your way up until you can count four chuffs for each full circle of the main crank.
Hint: when the range of possible values for a CV in a given decoder is large, often at 255 for a highest value, it is not worth changing your inputs when you are fiddling with them by values less than about 20 when you first start. Soon, you will deduce that you have overshot the ideal value. When this happens, use an old artillery trick. Halve the last added amount and deduct that from the current setting. Often that is all it takes to get really close. And in the artillery, which is an area weapon, close counts....a lot!
I've only watched once so far, but I'm pretty sure it traverses the same area, going in different directions, on a few occasions...... That seems to be a big "no-no" with many "modern" designs.....
