Similarly, Zimco Restaurants v. Bartenders Union (1958) involved a labor contract, apparently of no express duration, with employees of drive-in restaurants. The court declined to imply an intention of an indefinite duration; writing in 1958 with an astute prescience, the court noted "It is difficult to conceive that parties dealing with the business of drive-in restaurants intended a contract to last forever. The history of technological developments . . . in the organization of American industry has produced a modern miracle where change, not perpetual status, is the order of the day." (Zimco Restaurants v. Bartenders Union, supra, 165 Cal. App. 2d at p. 239. However, time and technological change are not always determinative. Zinn v. Ex-Cell-O Corp. (1957) 148 Cal. App. 2d 56 306 P.2d 1017, involved a detailed agreement for the distribution of milk machines. The court implied from the nature of the agreement and its circumstances that the parties intended a permanent contract terminable only for cause--the distributor could continue acting as such "as long as it performed the terms of the contract and the objects and purposes of the agreement could be served." (Id. at p. 73.) Among other factors, "the very nature and size of the undertaking which burdened the distributor once it executed the agency contract indicates that there was no intention that it should be terminable at will." (Id. at p. 74.) "Otherwise, plaintiffs could be denied the fruits of their labors even on the threshold of success. Equitable principles would prohibit such an oppressive result." (Ibid.)