COST AND UTILIZATION OF POWER ON FARMS. 
47 
The estimates of the 174 owners of 2-plow tractors and the 104 
owners of 3-plow tractors were as given in Table 31. 
It is seen that for each size the largest number estimated the life 
at 5 years. The wide range in the estimates was due not only to the 
condition of the tractors at the time of the investigation and the 
amount of work which would be done with them in the future but also 
to a considerable extent to each individual owner's idea as to when it 
would be more profitable to discard his tractor than to spend more 
time and money in keeping it in running order. 
The averages of the estimates for the 2-plow and 3-plow tractors 
of different ages are given in Table 32. There evidently was no tend- 
ency on the part of the men who had owned their machines only a 
short time to over-estimate the length of time their tractors would last. 
For each size the average of the estimates of the men who had owned 
their tractors 14 months or less; i. e., those who had done just one 
full year's work with them, was less than the average of all estimates. 
Table 32. — Estimated life of 2-plow and 3-plow tractors of different ages. 
2-plow tractors. 
3-plow tractors. 
Age of tractor (months). 
Num- 
ber. 
Esti- 
mated 
life 
(years). 
Num- 
ber. 
Esti- 
mated 
Ufe 
(years). 
14 and less 
74 
60 
28 
12 
6.3 
6.6 
6.5 
6.2 
29 
39 
20 
16 
6.6 
15 to 26 
7.2 
27 to 38 
7.0 
39 and over 
7.6 
All 
174 
6.4 
104 
7.0 
Depreciation. — The annual depreciation charge for each tractor was 
determined by dividing its first cost by the owner's estimate of its 
life. The wide range in the estimated life necessarily caused a wide 
range in the annual depreciation charges for the different machines, 
but this method is probably the best available, and the average deter- 
mined in this way will at least show the importance of this item of 
cost. 
The average annual depreciation for all tractors was $185. For 
2-plow tractors it was $164, and for the 3-plow $217. For most of 
the machines this charge was the greatest single item of cost con- 
nected with their use. 
Repairs. — The average amount which was spent during the year 
on the 286 machines for repairs, including both the cost of parts and 
the cash outlay for labor, was $29.95. The costs for 2-plow and 
3-plow tractors of different ages are shown in Table 33. The cost for 
the year was $20 or less for over half the machines in each age group, 
and the greater average cost for the older tractors was due to high 
