COST AND UTILIZATION OF POWER ON FARMS. 
Table 35. — Unpaid labor used in repairing tractors. 
49 
Labor used (days). 
Tractors on which 
specified amounts 
of labor were 
used. 
2-plow 
tractors. 
3-plow 
tractors . 

49 
41 
47 
16 
10 
11 
28 
1 
29 
2. 
17 
3 
12 
4 
9 
9 
Nearly all of the men who spent more than one or two days on 
repair work gave their machines a general overhauling during the 
year. 
The value of this labor at $5 per day has been included in the cost of 
operating the tractors Five dollars per day, or 50 cents per hour, is 
considerably higher than the value of ordinary farm labor during the 
year of investigation, but is considerably lower than the prices charged 
by regular experts and repair men. On the average this charge 
amounted to $8.55 for the 2-plow tractors, $9.45 for the 3-plow trac- 
tors, and $9.06 for all tractors. 
Interest. — Interest is charged at 6 per cent on the average invest- 
ment. The average investment has been found by the rule: 
Average investment = 
first cost X (years of service + 1 .) 
years of service X 2. 
This is the generally accepted formula for determining the average 
investment in equipment where a fraction of the first cost is charged 
off each year for depreciation. The interest charge when computed 
on this basis is slightly greater than when computed on one-half of 
the first cost. 
The average interest charge for the 2-plow tractors was $34, for 
the 3-plow $47, and for all tractors $40. 
Fuel and oil. — The average amounts of fuel and oil used per day 
by the 2-plow machines at the different drawbar operations are given 
in Table 36 and the amounts used by the 3-plow tractors in Table 37. 
The fuel and oil required per day by the 3-plow tractors was consid- 
erably greater for every operation than that required by the 2-plow 
machines, but this was offset by the greater number of acres covered 
per day by the larger machines (see Table 12), so that there was 
practically no difference in the requirements per acre between the 
2-plow and the 3-plow machines for any of the operations. 
