SE EP496.3 FEB2006 gricultural Machinery Management S T N D R D SBE i a profeional and technical organization, of member worldwide, who are dedicated to advancement of engineering applicable to agricultural, food, and biological ytem. SBE Standard are conenu document developed and adopted by the merican Society of gricultural and Biological Engineer to meet tandardization need within the cope of the Society; principally agricultural field equipment, farmtead equipment, tructure, oil and water reource management, turf and landcape equipment, foret engineering, food and proce engineering, electric power application, plant and animal environment, and wate management. NOTE: SBE Standard, Engineering Practice, and Data are informational and adviory only. Their ue by anyone engaged in indutry or trade i entirely voluntary. The SBE aume no reponibility for reult attributable to the application of SBE Standard, Engineering Practice, and Data. Conformity doe not enure compliance with applicable ordinance, law and regulation. Propective uer are reponible for protecting themelve againt liability for infringement of patent. SBE Standard, Engineering Practice, and Data initially approved prior to the ociety name change in July of 2005 are deignated a SE, regardle of the reviion approval date. Newly developed Standard, Engineering Practice and Data approved after July of 2005 are deignated a SBE. Standard deignated a NSI are merican National Standard a are all ISO adoption publihed by SBE. doption a an merican National Standard require verification by NSI that the requirement for due proce, conenu, and other criteria for approval have been met by SBE. Conenu i etablihed when, in the judgment of the NSI Board of Standard Review, ubtantial agreement ha been reached by directly and materially affected interet. Subtantial agreement mean much more than a imple majority, but not necearily unanimity. Conenu require that all view and objection be conidered, and that a concerted effort be made toward their reolution. CUTION NOTICE: SBE and NSI tandard may be revied or withdrawn at any time. dditionally, procedure of SBE require that action be taken periodically to reaffirm, revie, or withdraw each tandard. Copyright merican Society of gricultural and Biological Engineer. ll right reerved. SBE, 2950 Nile Road, St. Joeph, MI 49085-9659, US ph. 269-429-0300, fax 269-429-3852, hq@aabe.org
SE EP496.3 FEB2006 gricultural Machinery Management Propoed by the SE Farm Machinery Management Committee; approved by the Power and Machinery Diviion Standard Committee; adopted by SE December 1977 a EP391; revied editorially September 1979; reconfirmed December 1982; revied December 1983; reconfirmed December 1988; revied March 1990 and redeignated EP496; revied March 1993, March 1994; reaffirmed December 1998; revied editorially March 1999; reaffirmed December 1999, January 2001, December 2001, February 2003; revied February 2006. 1 Purpoe and cope 1.1 Purpoe. Thi Engineering Practice i intended to provide thoe who manage agricultural machinery operation with aitance in uing available data to determine optimum practice. It i intended that correponding claue in SE D497 be ued in claue 3, 4, 5, 6, 7, and 8 of thi Engineering Practice. Term ued in thi Engineering Practice are defined in SE S495. 1.2 Scope. Thi Engineering Practice include information helpful in making management deciion involving machine power requirement, capacitie, cot, election, and replacement. 2 Normative reference The following tandard contain proviion which, through reference in thi text, contitute proviion of thi Engineering Practice. t the time of publication, the edition indicated were valid. ll tandard are ubject to reviion, and partie to agreement baed on thi Engineering Practice are encouraged to invetigate the poibility of applying the mot recent edition of the tandard indicated below. Standard organization maintain regiter of currently valid tandard. 2.1 NSI/SE S296.5, General Terminology for Traction of gricultural Traction and Tranport Device and Vehicle 2.2 SE S495.1 Uniform Terminology for gricultural Machinery Management 2.3 SE D497.5, gricultural Machinery Management Data 3 Tractor performance 3.1 Tractor ue internal combution engine to power farm machine. Power loe are experienced in exerting power through the drive wheel, the PTO haft, and the hydraulic ytem. Figure 1 illutrate the maximum mechanical power performance expected from a two-wheel, rear axle drive tractor with rubber tire on a level concrete urface. 3.2 Slippage of drive wheel (ee SE S296) on oil urface i a power lo. Thi travel reduction, or lip () i meaured a n 1 n 100 n 1 i lip, percent; i the advance under no load condition per wheel or track revolution, m(ft); i the advance under actual load condition per wheel or track revolution, m(ft). Expected lip value for a ingle-drive wheel can be calculated from SE D497 when the net pull and the dynamic wheel load are known. 3.3 drawbar power to axle power ratio, called tractive efficiency, TE, can be etimated for a complete tractor from figure 1 in SE D497, Figure 1 Maximum mechanical power performance expected SBE STNDRDS 2006 SE EP496.3 FEB2006 385
when the lip i known. Maximum TE i obtained with optimum lip range of: 4 8% for concrete; 8 10% for firm oil; 11 13% for tilled oil; 14 16% for oft oil and and. TE (and tire efficiency) of a ingle-drive wheel can be predicted from SE D497, claue 3. The performance of a tractor i made up of the um of the individual wheel performance. For a two-wheel rear drive tract the motion reitance of the front wheel ubtract from the net pull obtained from the two-drive wheel to produce the net tractor drawbar pull. 4 Power requirement 4.1 Implement (machine) power component 4.1.1 Drawbar power i power developed by the drive wheel or track and tranmitted through the hitch or drawbar to move an implement through or over the crop or oil. Draft i the total force parallel to the direction of travel required to propel the implement. It i the um of the oil and crop reitance and the implement motion reitance. D R c MR D i implement, draft, N (lbf); R c i oil and crop reitance, N (lbf); MR i total implement motion reitance, N (lbf). 4.1.1.1 Soil and crop reitance i the force parallel to the direction of travel reulting from the contact between the oil or crop and the working component of the implement. Typical value of unit oil and crop reitance force are given in SE D497, claue 4. Soil and crop reitance for an implement i computed a R c nr c R c i oil and crop reitance for the implement, N lbf ; n i implement numeric coniting of total width, number of hank, cro-ectional area, number of row, etc., a required to balance the unit of the equation and depending on the unit of r c ; r c i unit oil and crop reitance pecific to the implement, a given in SE D497, claue 4. Thi value i the oil and crop reitance (alo called functional draft) of the implement parallel to the direction of travel. Thi value doe not include motion reitance. Unit depend on the pecific implement, and mut balance the unit of n. 4.1.1.2 Motion reitance (ee SE S296) become appreciable when heavy implement are ued in oft or looe oil. Value for the motion reitance ratio are predicted by SE D497, claue 3. Tire parameter and wheel loading mut be known or aumed. Total implement motion reitance i computed a MR R M MR i the total implement motion reitance, N lbf ; R M i motion reitance of each individual wheel upporting the implement, N (lbf). The motion reitance of each individual wheel can be computed a RM 9.8 m i motion reitance ratio (no unit); m i dynamic wheel load, kg; RM m i motion reitance ratio (no unit); m i dynamic wheel load, lb. 4.1.1.3 Drawbar power for tractor-powered implement (and propulion power for elf-propelled implement) i computed a P db D 3.6 P db D i drawbar power required for the implement, kw; i implement draft, kn; i travel peed, km/h; P db D 375 P db i drawbar power required for the implement, hp; D i implement draft, lb; i travel peed, mph. 4.1.2 Power-takeoff, PTO, power i power required by the implement from the PTO haft of the tractor or engine. Typical PTO power requirement can be determined uing rotary power requirement parameter given in SE D497, claue 4. Implement power take-off power can be calculated a P pto a bw cf P pto i power-takeoff power required by the implement kw (hp); w i implement working width, m (ft); F i material feed rate, t/h(ton/h) wet bai; a, b, and c are machine pecific parameter (SE D497, table 2). 4.1.3 Hydraulic power i the fluid power required by the implement from the hydraulic ytem of the tractor or engine. Implement hydraulic power requirement can be computed a P hyd pf 1000 P hyd F p i hydraulic power required by the implement, kw; i fluid flow, L/; i fluid preure, kpa; P hyd pf 1714 P hyd F p i hydraulic power required by the implement, hp; i fluid flow gal/min; i fluid preure, pi. 386 SE EP496.3 FEB2006 SBE STNDRDS 2006
4.1.4 Electric power i required to operate component of ome implement. Implement electric power requirement can be computed a P el IE 1000 P el i electric power required by the implement, kw; I i electric current, ; E i electric potential, V; P el IE 746 P el i electric power required by the implement, hp; I i electric current, ; E i electric potential, V; 4.2 Total power requirement for operating implement (drawn or elfpropelled) i the um of implement power component converted to equivalent PTO power. Total implement power requirement can be computed a P T P db P E m E pto P hyd P el t P T E t P db P hyd P pto P el E m i total implement power requirement, kw (hp); i tractive efficiency (expreed a a decimal) (ee SE D497, claue3); i drawbar power required for the implement, kw (hp); i hydraulic power required by the implement, kw (hp); i power-takeoff power required by the implement, kw (hp); i electric power required by the implement, kw (hp); i mechanical efficiency of the tranmiion and power train. Thi coefficient i typically 0.96 for tractor with gear tranmiion. 4.3 Total engine power mut be greater than the total implement power required. dditional power i required to accelerate and overcome change in topography, oil and crop condition. dditional power i alo required for operator-related equipment uch a hydraulic control ytem, air conditioning, etc. When electing the appropriate tractor for an operation, allow an additional 20% of the power requirement for reerve power. 5 Field machine performance 5.1 Field efficiency (ee SE S495) i the ratio between the productivity of a machine under field condition and the theoretical maximum productivity. Field efficiency account for failure to utilize the theoretical operating width of the machine; time lot becaue of operator capability, habit and operating policy; and field characteritic. Travel to and from a field, major repair, preventive maintenance, and daily ervice activitie are not included in field time or field efficiency. Field efficiency i not a contant for a particular machine, but varie with the ize and hape of the field, pattern of field operation, crop yield, crop moiture, and other condition. The following activitie account for the majority of time lot in the field: turning and idle travel; material handling; eed; fertilizer; chemical; water; harveted material; cleaning clogged equipment; machine adjutment; lubrication and refueling (beide daily ervice); 5.2 Effective field capacity i a function of field peed, machine working width, field efficiency, and unit yield of the field. rea capacity i expreed a C a we f 10 C a i area capacity, ha/h; i field peed, km/h; w i implement working width, m; E f i field efficiency, decimal; C a we f 8.25 C a w E f i area capacity, acre/h; i field peed, mile/h; i implement working width, ft; i field efficiency, decimal. Effective material capacity i expreed a C m C a y C m y i material capacity, t/h; i the average yield of the field in t/ha or ton/acre correponding to the unit of C a ; Typical range of field efficiency and field peed can be found in SE D497, claue 5. Theoretical field capacity can be determined by uing a field efficiency of 1.0. 5.3 The ability of a manager to make good ue of peronal working hour and thoe of employee i evaluated a cheduling efficiency. For example, if a workday i 10 h long and 8 h are ued effectively, the cheduling efficiency i 80%. Ineffective cheduling require larger capacity machine than are really neceary and increae capital invetment. 5.4 Performance of machine operated by ground wheel drive depend on the amount of lippage experienced between the tire and the ground urface. correction for lippage may be needed to predict performance of planter, grain drill, and other metering and rate application machine. 6 Cot of ue 6.1 Cot factor. The total cot of uing a field machine include charge for ownerhip and operation. Ownerhip cot are eemingly independent of ue and are often called fixed cot or overhead cot. Cot for operation vary directly with the amount of ue and are often called variable cot. 6.2 Ownerhip cot 6.2.1 Depreciation. Thi cot reflect the reduction in value of an aet with ue and time. The actual total depreciation can never be known until the equipment ha been old; however, an etimated depreciation can be predicted from any of everal method. Different computational method SBE STNDRDS 2006 SE EP496.3 FEB2006 387
are ued depending upon the objective. (For more detailed information conult an engineering economic textbook.) 6.2.1.1 To predict cot for crop production accounting, depreciation may be pread evenly over the accumulated ue of the equipment in hectare (acre) or hour. Simple annual depreciation i determined by ubtracting the alvage value from the purchae price and dividing by the anticipated length of time owned. 6.2.1.2 current market value help etimate depreciation. Several publication report uch value; example include: Official Guide Tractor and Farm Equipment and Farm Equipment Guide, Monthly Update. Thee on-farm remaining value are approximated a percentage of the lit price for the end of each year (ee SE D497, claue 6). Inflation and equipment hortage and urplue in the market place caue wide variation in thee predicted remaining value. The price of ued equipment after being reconditioned by a dealer may be 1.3 time the on-farm value. 6.2.2 Interet. n interet charge for the ue of the money in a machine invetment i an ownerhip cot. Simple interet on the average invetment over the life of the machine can be added to the annual depreciation to etimate the yearly capital cot of ownerhip (ee claue 6.2.4). method for determining the capital cot of ownerhip which include the time value of money make ue of a Capital Recovery Fact CRF. The invetment in the machine i multiplied by the proper CRF to give a erie of equal payment over the life of the machine which include both the cot of depreciation and interet. R P S q i 1 1 q i nq S q i R i one of a erie of equal payment due at the end of each compounding period, q time per year; P i principal amount; i i annual interet rate, decimal; q i compounding period per year n i life of the invetment in year; S i alvage value. 6.2.3 Other ownerhip cot. Taxe, houing, and inurance can be etimated a percentage of the purchae price. If the actual data are not known, the following percentage can be ued: taxe 1.00; houing 0.75; inurance 0.25; total 2.00% of purchae price. 6.2.4 Total annual ownerhip cot. imple etimate of total annual ownerhip cot i given by multiplying the purchae price of the machine by the ownerhip cot percentage expreed in decimal form. The ownerhip cot percentage can be calculated a C o 100 1 S v 1 S v i K L 2 2 C o i ownerhip cot percentage. Multiplying thi value, expreed in decimal form (i.e. C 0 /100), by the machine purchae price yield the average annual total ownerhip cot of the machine; S v i alvage value factor of machine at end of machine life (year L), decimal; L i machine life, yr; i i annual interet rate, decimal; K 2 i ownerhip cot factor for taxe, houing, and inurance; normally expreed a a percentage of the purchae price, but expreed in decimal form in thi equation. 6.3 Operating cot 6.3.1 Repair and maintenance. Expenditure are neceary to keep a machine operable due to wear, part failure, accident, and natural deterioration. The cot for repairing a machine are highly variable. Good management may keep cot low. Indice of repair and maintenance cot are hown in SE D497, claue 6. The ize of the machine, a reflected by it lit price, and the amount of ue are factor affecting the cot. Both the ue and cot are expreed in an accumulated mode to reduce variability. In time of rapid inflation, the lit price mut be increaed to reflect inflation effect. ccumulated repair and maintenance cot at a typical field peed can be determined with the following relationhip uing the repair and maintenance factor RF1 and RF2 (ee SE D497, claue 6) and the accumulated ue of the machine: RF2 h C rm RF1 P 1000 C rm i accumulated repair and maintenance cot, dollar; RF1 and RF2 are repair and maintenance factor (ee SE D497, claue 6); P i machine lit price in current dollar. In time of rapid inflation, the original lit price mut be multiplied by (1 I) n where I i the average inflation rate and n i the age of the machine; h i accumulated ue of machine, h. Thi relationhip provide an etimate of the total cot of all replacement part, material, hop expene, and labor for maintaining a machine in good working condition. ctual cot may vary widely due to difference in machine maintenance, management, and quality. Data hould not be extrapolated beyond the etimated life of the machine. Etimated life i the level of accumulated ue where further repair of the machine i normally not jutified. For machine ued beyond the etimated life, accumulated repair and maintenance cot can be aumed to increae at a contant rate equal to the rate at the end of it etimated life. an example of the ue of thee indice, the accumulated repair and maintenance cot for a $12,000 mower-conditioner ued 1200 h would be: C rm 0.18 12000 1000 1200 1.6 C rm i $2891 for an average-to-date cot of $2.41/h. 6.3.2 Fuel 6.3.2.1 verage fuel conumption for tractor. nnual average fuel requirement for tractor may be ued in calculating overall machinery cot for a particular enterprie. However, in determining the cot for a particular operation uch a plowing, the fuel requirement hould be baed on the actual power required. 388 SE EP496.3 FEB2006 SBE STNDRDS 2006
6.3.2.1.1 verage annual fuel conumption for a pecific make and model tractor can be approximated from the Nebraka Tractor Tet Data. verage gaoline conumption over a whole year can be etimated by the following formula: Q avg 0.305 P pto Q avg P pto i average gaoline conumption, L/h; i maximum PTO power, kw; Q avg 0.06 P pto Q avg P pto i average gaoline conumption, gal/h; i maximum PTO power, hp. 6.3.2.1.2 dieel tractor will ue approximately 73% a much fuel in volume a a gaoline tract and liquefied petroleum LP, ga tractor will ue approximately 120% a much. 6.3.2.1.3 Fuel conumption for engine not included in the Nebraka Tractor Tet Data may be etimated by the above formula by ubtituting the advertied PTO power, kw (hp), for the maximum PTO power, kw (hp), or by comparing them with a tractor engine of imilar diplacement. 6.3.2.2 Fuel conumption for a pecific operation. Predicting fuel conumption for a pecific operation require determination of the total tractor power for that operation (ee claue 4). The equivalent PTO power i then divided by the rated maximum to get a percent load for the engine. The fuel conumption at that load i obtained from SE D497, claue 3. Fuel conumption for a particular operation can be etimated by the following calculation: Q i Q P T Q i i etimated fuel conumption for a particular operation L/h (gal/h); Q i pecific fuel conumption for the given tract determined from SE D497, claue 3, L/kW h (gal/hp h); P T i total tractor power (PTO equivalent) for the particular operation kw (hp). fuel conumption of 15% above that for Nebraka Tractor Tet i included for lo of efficiency under field condition. 6.3.3 Engine oil conumption i baed on 100-h oil change interval. The conumption rate of oil range from 0.0378 to 0.0946 L/h (0.01 to 0.025 gal/h) depending upon the volume of the engine crankcae capacity. If oil filter are changed every econd oil change, total engine lubrication cot approache 15% of total fuel cot. Uually the cot of filter and the cot of oil other than crankcae oil i included a maintenance cot. For oil conumption a related to engine ize, ee SE D497, claue 3. 6.3.4 Labor cot. The cot of labor varie with geographic location. For owner-operator, labor cot hould be determined from alternative opportunitie for ue of time. For hired operator, a contant hourly rate i appropriate. In no intance hould the charge be le than a typical, community labor rate. 6.3.5 portion of the tractor ownerhip cot mut be included in the cot of ue of implement. Tractor ownerhip cot are recovered by aeing thoe operation that ue the tractor. eing may be done on an energy ue bai, but i more commonly done on a time bai. For example: If a tractor ha $1000 of ownerhip cot per year and i ued 500 h annually, a $2 charge i made againt the implement operation for each hour the tractor power the implement. Implement not uing a tractor (elf-propelled) do not have uch a cot. 7 Reliability 7.1 Operational reliability i defined a the tatitical probability that a machine will function atifactorily under pecified condition at any given time. The operational reliability i computed a one minu the probability for downtime when both probabilitie are in decimal form. The reliability probability for the next minute of machine operation i eentially one, but decreae when the time pan under conideration lengthen. The probability of having a complex machine continually operational for everal eaon on a large farm i eentially zero. 7.2 The reliability of a combination of component or machine i the product of the individual probabilitie. Complex machine with many component mut have very high individual component reliabilitie to achieve atifactory operational reliability. 7.3 Survey of field breakdown a reported in SE D497, claue 7, indicate expected reliability for everal field operation. 8 Selection of field machine capacity 8.1 Simple capacity election i made by etimating the number of day in the time pan within which the operation hould be accomplihed, and by determining the probability of a working day in thi time pan (ee SE D497). The required capacity for an area i C i BG pwd C i B G i required machine capacity, ha/h (acre/hr); i area, ha (acre); i number of day within the time pan within which the operation hould be accomplihed, day; i expected time available for field work each day, h/day; pwd i the probability of a working day, decimal. 8.2 Economic election find that capacity which produce the lowet net cot. The increaed ownerhip cot of high capacity machine are balanced againt the increaed operation cot and timeline cot of low capacity machine. 8.2.1 unit price function mut be determined which reflect the increaed price of one unit of increaed capacity. On many machine, the price of a unit increae in effective width i linear and directly related to price per capacity. The unit price function can be calculated a follow: K p 10P w E f K p P w E f i the unit price function which reflect the increaed price of one unit of increaed capacity, dollar/ha h; i field peed, km/h; i price per unit width of increaed width of machine, dollar/m, i field efficiency, decimal; K p 8.25P w E f K p P w E f i unit price function which reflect the increaed price of one unit of increaed capacity, dollar/acre h; i field peed, mph; i price per unit width of increaed width of machine, dollar/ft; i field efficiency, decimal. SBE STNDRDS 2006 SE EP496.3 FEB2006 389
8.2.2 If fuel, oil, and repair and maintenance cot can be aumed to be function of field area covered, they are not pertinent to the election problem and can be ignored. Only a labor cot, L c, dollar/h, and a tractor ownerhip cot, T fc, dollar/h, are important to the operation cot. T fc equal zero for elf-propelled machine. 8.2.3 The timeline cot i etimated from a timeline coefficient obtained from SE D497, claue 8. The annual timeline cot for an operation can be etimated by W K 3 2 YV ZGC i pwd W i annual timeline cot, dollar; K 3 i timeline coefficient obtained from SE D497, claue 8; i area, ha (acre); Y i yield per area, t/ha (ton/acre); V i value per yield, dollar/t (dollar/ton); Z i 4 if the operation can be balanced evenly about the optimum time, and a value of 2 if the operation either commence or terminate at the optimum time; G i expected time available for field work each day, h; pwd i probability of a working day, decimal; i machine capacity, ha/h (acre/h). C i 8.2.4 The optimum capacity of a machine can be etimated from the firt differential of the annual cot with repect to the machine capacity M oc 100 C o K p L c T fc K 3YV ZG pwd M oc i optimum capacity of a machine, ha/h (acre/h); i area, ha (acre); C o i ownerhip cot percentage, percent; K p i unit price function, dollar/ha h (dollar/acre h); L c i labor cot, dollar/ha (dollar/acre); T fc i tractor ownerhip cot, dollar/ha (dollar/acre); K 3 i timeline coefficient obtained from SE D497, claue 8; i area, ha (acre); Y i yield per area, t/ha (ton/acre); V i value per yield, dollar/t (dollar/ton); Z i 4 if the operation can be balanced evenly about the optimum time, and a value of 2 if the operation either commence or terminate at the optimum time; G i expected time available for field work each day, h; pwd i probability of a working day, decimal. an example, conider the required capacity for a field cultivator having a unit price function of $400 per ha per h, a 16% ownerhip cot percentage, ued on 200 ha twice each year. Labor and tractor ownerhip cot per ha are $3 each. The crop ha a value, YV, of $150 per ha, and there are 10 field working hour per day at a probability of 0.8. The operation will be balanced about the optimum time (Z 4) and the value of K 3 i elected a 0.0002. M oc 2 100 200 3 3 0.0002 200 150 16 400 4 10 0.8 6.2 ha/h If field peed i expected to be 8 km/h and the field efficiency 0.80, the width of the field cultivator would be C a WE f 10 6.2 8 W 0.80 10 width i 9.7 m. 8.3 The election of a machine ytem involve the election of tractor and their aociated machine which give leat cot when both timeline and cheduling factor are conidered. Except for the implet of ytem, uch election are accomplihed with digital computer program. 9 Replacement 9.1 Machine employed in production may need to be replaced for one or more reaon. 9.1.1 machine uffer accidental damage uch that the cot of renewal i o great that a new machine i more economical. 9.1.2 The capacity of the exiting machine i inadequate becaue of increaed cale of production. 9.1.3 The machine i obolete (ee SE S495). 9.1.4 The machine i not expected to operate reliably. (Suffer coniderable unanticipated downtime from random part failure). 9.1.5 The cot of making an anticipated repair would increae the average unit accumulated cot (ee SE S495) above the expected minimum. Only capital cot and actual repair and maintenance cot need be accumulated. For example, a $3000 machine i ued 100 ha annually. It experience the following end-of-year depreciation, interet (8% imple interet on average invetment), and actual repair and maintenance cot lited in table 1. Year 9 ha the lowet unit cot and indicate the machine hould be replaced with a imilar machine at the end of year 9 if not before for other reaon. Inflation effect mut be conidered in making replacement deciion. nnual depreciation charge may be quite low or even negative in time of rapid inflation producing a premature minimum unit accumulated cot. In uch intance replacement i better indicated by comparing the unit accumulated cot of the preent machine with the projected cot for a potential ucceor machine. Optimum replacement time may be delayed beyond that time determined under more table economic condition. nnex (informative) Bibliography The following document are cited a reference ource ued in development of thi Engineering Practice: Farm Equipment Guide, Monthly Update. Fort Dodge: Hot Line, Inc. Nebraka Tractor Tet Data. Lincoln: Univ. of Nebraka Biol. Sy. Eng. Dept. Official Guide-Tractor and Farm Equipment. St. Loui: North merican Equipment Dealer n. 390 SE EP496.3 FEB2006 SBE STNDRDS 2006