That farmers of Iowa make an extensive use of farm machines is indicated by the 16th Census of the United States which gives the value of farm implements and machinery on Iowa farms, April 1, 1940, as $242,047,158. This is about one-twelfth of the total for the United States and represents an investment of $1,134 for each Iowa farm. Under these circumstances it is recognized that the use of farm machines occupies an important role in the agricultural practices of the state. Farm machines not only give the farm workers control over large units of power, thus making possible large individual productive capacity, but they also make farm labor less arduous. For these reasons the cost of farm-machine service or use as discussed in this bulletin should be of general interest.