Of course, this method was not mathematically accurate, as the condition
of track, the weather, and the personal equation of the locomotive
engineers all had an effect, but, later, when correcting the rating by
tests with dynamometers, it was found that the results were fairly
practical.

There were three hills where the rate of grade was the same as the rest
of the division, but where the length was much in excess of other grades
of the same rate.

Designating these hills as _A_, _B_, and _C_, the lengths are,
respectively, 2.44, 3.57, and 4.41 miles. There were no other grades of
the same rate exceeding 1 mile.

In one class of freight engines, 10-wheel Brooks, the weight of the
engine was 197,900 lb.; tender, 132,800 lb.; weight on drivers, 142,600
lb.; boiler pressure, 200 lb.; and tractive power of cylinders, 33,300
lb.

On Hill _A_ these engines are rated at 865 tons, as compared with 945 on
other parts of the division. As the engine weighs 165 tons and the
caboose 15 tons, 180 tons should be added, making the figures, 1,045 and
1,125 tons. Thus the length of the grade, 2.44 miles, makes the tractive
power on it 92% of that on shorter grades.

On Hill _B_, the rating, adding 180 tons as above, is 1,160 and 1,230
tons, respectively, giving 94% for 3.57 miles.

On Hill _C_, the rating, with 180 tons added, is 1,130 and 1,230 tons,
making 92% for 4.41 miles.