الفهرس 
ACKNOWLEDGMENTOnly 14 pages are availabe for public view
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Abstract
Repair and maintenance of tractors and agricultural machinery must be taken care of so as to reduce operating costs and reduce hours of breakdowns. It is necessary to calculate the remaining value of tractors and agricultural machinery from time to time because if the repair and maintenance costs exceed the fixed cost of the machinery. High remaining value of the using machine helps to purchasing new machinery. It also reduces the number of hours the crop is planted, which reduces the crop loss due to the lack of timely machinery planting. After analyzing the results obtained and statistical analysis of the previous equations we can recommend the use of the coefficients obtained from that study, as they fit with the conditions of Egyptian agriculture and more realistic in calculating the value of repair and maintenance, and the remaining value of the machinery and its relationship to the best time to replace the machinery with another new, as well as Less timeliness cost. This research was aimed to cover these points: 1-Restudying and adopted repair and maintenance equation coefficients to be used under Egyptian condition. 2-Related the replacement of machine to remain value, with adjusting the remaining value equation coefficients. 3-Machine sizes and operational available spans time affected the crop net return. Timeliness equation coefficients were adjusted for famous Egyptian crops, for maximum crop yield to avoid the early or late establishment crop yield losses. 4-Adjusting the previous equation coefficients under Egyptian condition may be easily inclusive in any farm machinery operating and project.