Steam engine question

[Sumpter250]

Holes in the fire. These are places where, for whatever reason, there's little or no combustible material.
Hand firing's most critical concern is getting the coal evenly distributed across the grate, and avoiding "holes" in the fire.
These "cold spots" reduce the loco's fuel/steam efficiency.

Don't knock the slide rule, they can do things a lot of modern calculators don't always have the programs to do. What amazes me even more is with the limited diagnostic equipment of the day, how they figured out what was going on, and why, before they could begin to figure out what to do about it.

Another fascinating subject, is exactly how a steam locomotive's equalized suspension works!, and just how precise all the parts have to be, to do the job correctly, while still supporting the tons of weight! Side rod binding in a model is inconvenient......in the prototype it was disastrous!